Perhaps more than any other genre of television, the success of all sitcoms relies heavily on its casting from the very beginning.

While it's true that the chemistry between a cast is key to the success of any product, whether on the big or small screen or even on the stage, there's no denying that sitcoms have an added burden to take into consideration.

Some people just aren't meant to be funny for any considerable amount of time. Other people are funny on their own, but have a hard time playing well off others.

Sometimes, shows are lucky enough to find the perfect comedic duo or trio or even larger group on the first go around in the casting process -- but that's a rare feat that few can lay claim to.

Sitcoms also occasionally film in front of live studio audiences and test panels. If the viewers don't respond well to the way in which two actors play off each other, or don't feel that the core group of characters gels correctly, then there is usually substantial revision behind the scenes in the form of re-casting, coaching, rewriting, and countless more creative avenues.

Certain sitcoms clearly have breakaway stars who come to represent the series all on their own, while others are an ensemble performance from day one onward.

However, unfortunately, there are also sitcoms where a single unaddressed miscasting totally affected the quality of the show overall, preventing it from reaching its potential peak quality.

Here are the 10 Casting Decisions That Hurt Iconic Sitcoms (And 10 That Saved Them).

Hurt: Elizabeth Berkley (Saved by the Bell)

Jessie Spano may be responsible for one of the most iconic (albeit infamous) scenes in Saved by the Bell history, but it’s not exactly due to the acting talent in that scene that the moment has become so well-known.

Elizabeth Berkley played Jessie Spano across the high school years of the Saved by the Bell franchise, an uptight perfectionist and overachiever who usually screams and insults her way into getting what she wants.

While Berkley would go on to have a role that would earn her more derision in Showgirls, there’s no denying that her turn as Jessie wasn’t exactly award worthy material.

This is especially the case with the now viral “I’m so excited” scene, in which she screams her way through a heightened period of some Saturday morning friendly version of overdose and withdrawal all at once.

Saved: Tracy Morgan (30 Rock)

Some characters blur the lines between parody and reality so wonderfully that it becomes difficult to imagine the actor as anyone but their on screen persona.

Tracy Morgan’s stand up personality, as well as his roles in other movies and advertisements, are virtually impossible to distinguish from his 30 Rock character, Tracy Jordan, at times.

However, that in itself is part of what makes the genius of both Tracy Morgan and Tracy Jordan so wonderful.

Bumbling but lovable, well-intentioned but often lacking the forethought for planning and follow through, Tracy Jordan is the unlikely heart of the world of 30 Rock in some ways, providing a real foil for the business-minded world that Liz and Jack inhabit.

Tracy Jordan lives in a totally different world – and through Morgan’s comedic genius, it’s not too hard to want to live in that world, too.

Hurt: Josh Radnor (How I Met Your Mother)

It’s often the case with ensemble sitcoms that the alleged main character winds up being the most boring one of the bunch.

However, an unfortunate cooccurrence that has become all too common with recent sitcoms is that, not only is the lead character the most boring of them all, but he or she is also almost unbearably awful.

Take, for example, Ted Mosby from How I Met Your Mother. It would be one thing if Ted’s general ick factor were acknowledged and not played off for laughs.

It’s possible to have an antihero at the heart of your sitcom – some of the best sitcoms in the peak TV era excelled at just that.

However, with Josh Radnor trying (and often failing) to play Ted as a winning, sympathetic character, and not a totally selfish and often unprofessional and cruel mess, the series misses the mark – again, and again, and again.

Saved: Eden Sher (The Middle)

In a television landscape full of increasingly cynical, angry, awful people, it’s hard to be a ray of sunshine through increasingly bleak clouds. However, for nine seasons (and now, with the potential for a spinoff of her own), Eden Sher was able to do just that.

The Middle has long been one of television’s most underrated, steadily performing sitcoms.

However, among all of its overlooked greatness, Eden Sher’s Sue Heck is by far its strongest success story.

Optimistic to a fault, kind and compassionate despite herself, and always willing to do whatever she can to help, Sue Heck is the kind of character you rarely ever see in a story ostensibly about real life.

However, even in moments when Sue’s cheeriness could border on grating, Sher’s performance was faultless.

As she grew from a young teen to an adult, both onscreen and offscreen, Sher’s talents only blossomed further, creating a richer journey through the middle with Sue.

Hurt: Daphne Maxwell-Reid (The Fresh Prince of Bel-Air)

Re-casting a role mid-series always makes for an awkward situation. Does the series acknowledge the change of appearance in a tongue in cheek way? Do they just move on as if nothing happened?

The original Aunt Viv on The Fresh Prince of Bel-Air – played with poise, grace, wit, and warmth by Janet Hubert in the series’ first three seasons – was everything an inspirational matriarch on television should be.

She was a leader of the household, a compassionate mother, a loving partner, a proud professional, and so much more.

However, following Hubert’s departure from the series, the role was recast with Daphne Maxwell-Reid.

Though she is a talented actress in her own right, she is also a woman so woefully miscast as the previously inspirational Aunt Viv that they may as well have just pretended she was a new character altogether, rather than strain at making any semblance of a connection between the two.

Saved: Tituss Burgess (Unbreakable Kimmy Schmidt)

Having a character created for you is one of the ultimate forms of flattery for an actor. It's also a sign of the amazing talent that audiences everywhere will soon be exposed to.

Look no further than Unbreakable Kimmy Schmidt's diva extraordinaire, Titus Andromedon, for the prime example of this feat.

As the breakout character of the series by far, Titus has proven himself to be a true cultural icon -- coining catchphrases, musical parodies, and even taking on Beyoncé's Lemonade with great success.

However, none of this would have been possible had the role not been crafted for the otherworldly talent of Tituss Burgess. Previously a supporting player on 30 Rock, and a longtime star of the theatre, Burgess officially launched his star into the Hollywood world through his deeply passionate and wonderfully unique portrayal of Titus Andromedon.

Even daring to imagine anyone else in the role is unthinkable.

Hurt: Paul Schneider (Parks and Recreation)

Let’s be real here: all of you Parks and Rec fans out there, did you even remember that a character named Mark Brendanawicz once existed within the world of the show?

As an all-around jerk from the moment he stepped into the shiny world of Pawnee, Mark rarely did anything that didn’t have negative consequences for our Parks and Recreation crew.

Selfish and unfeeling more often than not, Mark just didn’t fit into the world of this tight knit group who came to care deeply for one another.

It also didn’t help that Paul Schneider was woefully miscast in the role.

Although rumors of behind-the-scenes issues persist, especially after his sudden departure at the end of season two, there’s no way of avoiding the fact that Schneider is far better off in dramatic roles than he is in comedic ones.

Saved: Susie Essman (Curb Your Enthusiasm)

Making an art form out of swearing, screaming, and snarking isn’t exactly something that most actors can pull off, no matter the level of profanity they’re willing to use or how red in the face they can get.

However, for her entire time on the irreverent, long-running HBO series Curb Your Enthusiasm, Susie Essman has stolen each and every scene she is in due to the precise, perfected balance of those three things.

Whether she’s screaming at Larry David’s clueless and bordering on sociopathic Larry, or railing against her idiotic husband, Jeff Garlin’s Jeff, Susie Essman is the star of the show, no matter how many uses of profanity she manages to get in one scene.

Hurt: Heidi Swedberg (Seinfeld)

It’s not every day you come across a sitcom character so universally hated that the series is able to get rid of them in as cruel and unsettling a way as Seinfeld did with George’s fiancée, Susan – and make the audience laugh about it.

Susan was a character who, simply put, never should have been introduced. Susan never fit in with any of the core group of four, even as she came closer and closer to marrying George.

According to Jason Alexander himself, difficulties behind-the-scenes with the actress only further enhanced the failure of Susan’s character as a whole.

However, it should be noted that Swedberg’s performance in no way fits the tone of the series.

Better casting could have allowed for interesting satirical humor at the expense of both Susan and the gang. However, with Swedberg in the role, nothing worked.

Saved: David Hyde Pierce (Frasier)

In less capable hands, a character like Niles Crane could have gotten very old, very fast.

As the textbook definition of neurotic, paranoid, and a hopeless romantic, Niles could have very easily been the punchline of Frasier’s story, a pathetic sap who no one dares take seriously because he’s simply so sad.

However, thanks to the game-changing performance by David Hyde Pierce, for 11 years, Niles remained one of television’s strongest, most fascinating, and most lovable male characters.

His quirks never became overwhelming, but were portrayed with whimsy and heart. His love for Daphne never came across as pathetic or over the top, but rather came across as bittersweet and worth rooting for.

Niles, in many ways, becomes the heart of the series over its lengthy run – and for a show that began as a spinoff due to the success of a character on another series, that’s truly a testament to the actor’s talent.

Hurt: Maggie Wheeler (Friends)

"Oh my god"-- the three words that make a chill run down the spine of any and all Friends fans everywhere, not to mention the characters themselves.

In her earliest appearances, Janice was amusing – a quirky outsider among the close-knit group with a larger than life personality and a louder than normal laugh.

However, with every subsequent appearance, Janice became more and more of a stereotype – a braying laugh and exclamation of those three little words and nothing more.

Maggie Wheeler’s performance began as something comical and light, but the more the series depended upon the easy touchstone references for Janice’s character in the later years, the more Wheeler’s performance descended into parody of her own work.

Saved: Julia Louis-Dreyfus (Veep)

What is there to say about Julia Louis Dreyfus that hasn’t already been said? Also, what is there to say about her tenure as Selina Meyer on the acclaimed HBO series Veep that six Emmy awards don’t already say?

For years, Julia Louis-Dreyfus has won the hearts of viewers everywhere with her unflappable comedic timing and earnest portrayals of characters who are, frankly, kind of a mess.

Whether Elaine Benes, Christine Campbell, or Selina Meyer herself, Louis-Dreyfus has shown, time and again, that she is the woman for the job – now more than ever before.

Selina has been put through the political and personal wringer in Veep’s six seasons, but Louis-Dreyfus has never faltered in her portrayal of the former Vice President-turned-President of the United States.

Hurt: Lisa Bonet (The Cosby Show)

With a family as large as the Huxtables’ on The Cosby Show, it’s a given that a few of the children are going to be annoying. Vanessa Huxtable may have been a brat, but it’s Denise Huxtable who is, far and away, the most unbearable of them all.

Denise gets all the storylines associated with flaky teenagers who refuse to grow up – even as she grows from adolescence to adulthood. However, she never ages past that artsy, absentminded girl we first meet in the pilot.

Complicating matters further is Lisa Bonet’s questionable turn as the character.

Bonet is often monotone to the point of inanity, with Denise’s sardonic comments being delivered as though they were being read off a sheet of paper.

Somehow, Bonet was the cast member chosen to launch her own spinoff series, A Different World. However, what really says it all is that the series would go on to be far more successful without her.

Saved: Ty Burrell (Modern Family)

The world of beloved sitcom parents is a very competitive and highly populated one – and one that is ever growing with each new TV season.

However, for the last nine years, one of the strongest contenders for the title of Best Dad On Television has been Modern Family’s Phil Dunphy.

Lovably dorky and just the right amount of oblivious, Phil brings light and warmth to even the dullest of Modern Family episodes, particularly in recent seasons.

Thanks to veteran comedic talent Ty Burrell, Phil has earned himself a rightful place in the television canon as one of the best of the best.

Through Burrell’s commitment to silliness, heart, and an impressive array of physical humor feats, Phil Dunphy’s character has become the center of this truly unconventional family unit.

Nine years in, we wouldn’t have it any other way.

Hurt: Chevy Chase (Community)

From the start, Community was a show about an unlikely group of totally different strangers coming together and finding some sort of community among one another in their college.

As they came from all walks of life, conflict often arose from differences in perspective and background.

However, from his introduction, the character of Pierce Hawthorne was a mistake.

Privileged, old world, and offensive in his out of date behaviors and opinions, the character stuck out like a sore thumb, despite the considerable comedic talent the series had recruited in the likes of Chevy Chase.

Rumors of behind-the -scenes difficulties between the legendary comedic star Chase and the those involved with the production quickly began to circulate -- so it's no wonder, really, that Pierce was written off in so unceremonious a way.

Saved: Jim Parsons (The Big Bang Theory)

When The Big Bang Theory first aired, it was clear that one character was going to stand out: Dr. Sheldon Cooper, portrayed by then relative newcomer Jim Parsons.

Over 11 seasons, Parsons has crafted in his portrayal of Sheldon, one of television's most fascinating, consistently hilarious characters.

As a caricature of the ultimate nerd, Parsons' Sheldon is just the right mix of aloof and caring, genius and oblivious, human but alien.

Nerds have had a real surge in popularity in the world of television and film in recent years, but The Big Bang Theory got in before the trend really started.

By being part of this movement from the ground up, Jim Parsons has shown himself to be a versatile actor capable of showing the development of a young scientist from a man child to a now slightly older and married man child.

Also, based on who Sheldon was when we met him in the pilot, it's safe to say that we doubted that this day would ever come.

Hurt: Josh Meyers (That '70s Show)

The most dedicated of That ‘70s Show fans rarely agree on a lot of things, but one opinion seems to be pretty common throughout the community: we don’t talk about the last season.

Whether you disagree with the direction Jackie’s character was taken, or Donna’s character, or Hyde or Kelso or whoever, the main complaint that crops up time and again is this: what on earth was the point of Randy?

Eric was gone, so the series decided to replace him with a bumbling idiot.

However, boy did they miss the mark on that one. Casting Josh Meyers in the role, That ‘70s Show created an utterly unsympathetic knockoff version of Eric without any of the hallmark heart and goofiness that made Eric Forman such an enjoyable character to begin with.

Randy would always feel as though he were a placeholder for Eric, just occupying space until Eric returned to reclaim his rightful place.

Saved: Sean Hayes (Will & Grace)

In its revolutionary primetime run, Will & Grace never parodied or looked down upon either Will or Jack due to their orientation. Eric McCormack was wonderfully earnest in his tenure as Will, and still is to this day in the revival.

However, it’s the showstopping, hysterics inducing performance by Sean Hayes that truly cemented the show’s legacy as one of the most influential and culturally relevant sitcoms of all time.

Jack is, quite literally, a phenomenon in human form – a force to be reckoned with in so many ways that it’s almost hard to decide where to start.

Yet, without Hayes’ passionate work as the aspiring star, Jack would be nothing like the icon he now is.

With effortless comedic timing, a willingness to engage in just the right amount of physical humor, and an endless supply of hidden heart, Hayes’ Jack is everything a sitcom character should be, and more.

Hurt: Zooey Deschanel (New Girl)

Once upon a time, Zooey Deschanel’s wide-eyed waif-like appeal was all the rage, with roles such as the female lead in (500) Days of Summer attesting to the fact.

However, when it comes to the case of New Girl, the sitcom she starred in for seven years, Deschanel was, by far, the weakest performer in the entire cast.

Surrounded by incredibly talented costars at every turn, Deschanel’s Jessica Day felt obnoxious far more than she ever did sympathetic. Whiny and entitled, Jess’s behavior causes most of the series’ problems, with little humorous enjoyment attached to them.

When surrounded by stellar supporting characters such as Nick, Winston, Schmidt, and Cece, there’s no way that this average ordinary new girl could compete.

Saved: Steve Carell (The Office)

Could you imagine anyone else playing Michael Scott?

Of course, The Office is, itself, a remake of the original UK version of The Office, which found Ricky Gervais in a similar role as David Brent.

However, as the US version of The Office ran for so much longer than its British counterpart, Michael’s character went so far beyond David’s in terms of development that comparing the two is, ultimately, useless.

Much of Michael’s development, and the sincerity of his character, can be attributed to Steve Carell’s masterclass of a performance.

Whether in moments of utter lack of self-awareness, bordering on insanity in his frank humor, or revealing the genuine kindness he has in his little boy-like heart, Carell’s Michael Scott is the kind of man everyone would be lucky to have in their lives.

Maybe he’s not exactly World’s Greatest Boss, but in the television landscape, he’s about as good as they get.

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Can you think of any other casting decisions that hurt or saved iconic sitcoms? Let us know in the comments!