Who's to say when the perfect time for a television show to end is? Do we base it off of seasons? Episodes? Or do some wells simply run deeper than others and certain characters are just destined to stick around on our television screens longer than others?

RELATED: 12 Iconic Sitcoms That Were Cancelled Too Soon (And 8 That Need To Go)

There's no secret formula to decide when a television show should end (unless a network decides to not renew it or cut it), but choosing when to do so can be a delicate matter and if done poorly can usually put the show's fanbase on a fence about how they feel regarding the entire series. But if done correctly, it often leads to the show forever being solidified as one of the greatest of all time. Here are five shows that knew when to call it quits, and five that ran themselves into the ground.

Perfect: Avatar: The Last Airbender

What's that? You didn't expect the number one show on this list to be an animated children's series that only has three seasons? That doesn't change the fact that it's rightfully earned the spot by being not only one of the greatest shows ever produced, but one of the most incredible stories ever shared with the world.

The 61 episode narrative of a 12-year-old boy who can manipulate all elements, and must learn to control and master those elements in less than a year to stop a tyrannical, fire-wielding overlord from taking over the world painted a pixel-picture the likes of which hadn't graced a television screen before. While the premise sounds like it deserves well more than a 61 episode run, the result was a show with arguably the most loyal fan-base in television, and the number one spot on our list.

Dragged On: The Big Bang Theory

Our whole universe was in a hot, dense state and then a sitcom about nerds ran for 14 billion years. The Big Bang itself might have been instantaneous but this CBS comedy refused to leave the air as it ran for a total of 12 seasons from 2007 to 2019, ending just this past May.

The show may have been a cultural phenomenon, but once the entire main group of guys all got girlfriends in the later seasons and the show stopped focusing on science, every episode became predictable and felt like Friends redux. The geeks in the beginning were great, but this show continued on for a few too many Bazingas.

Perfect: Parks & Recreation

Leslie and Ron talking on a park bench in Parks and Recreation

More often than not, comedies tend to be the biggest culprits when it comes to running too long, and it's not without reason. The characters aren't usually meant to grow much and having plots that don't ordinarily focus on gaining something lets the episodes and seasons be pretty open-ended. That's why Parks & Recreation was such a fresh take on mockumentary-style comedy when it decided to call it quits after the seventh season.

RELATED: 10 Canceled TV Shows We Never Got To See (And 10 That Went On Too Long)

Every character had an arc that showed them growing from a person we loved into a person we loved even more, and the creators knew that no amount of laughs could improve upon that. Leslie Knope/Ben Wyatt 2020.

Dragged On: Supernatural

The only thing that's supernatural about this show anymore is how it's still on the air. Seriously, it's almost impossible for a show that isn't a comedy to stick around for fourteen years, but somehow the Winchester brothers have managed to pull it off.

Having battled every monster known to man, including vampires, werewolves, skinwalkers, and shape-shifters, and doing so in places such as Hell and Purgatory themselves, it's hard to imagine what more the show could do. As it turns out, they think the same as their current (fifteenth) season will be their last. Sorry, Supernatural fans, but it's time for this show to finally R.I.P.

Perfect: The Wire

Stringer Bell looking serious in The Wire

Audiences may not have turned out in droves to watch The Wire when it first originally aired on television, but ironically that may have been what saved it from running too long, thus resulting in one of the greatest shows to ever bless the little screen. Focusing on a different institution within the city of Baltimore every season, critics and fans alike now highly praise this show for its accurate look into the unfortunate happenings of the day-to-day life of certain communities within our society.

But more than that, The Wire is regarded for showing audiences that the differences between these communities are marginally thin. While it might not have brought home any hardware, it earns a well-deserved spot on our list.

Dragged On: The Simpsons, South Park, Family Guy

Are they ever going to end?! 1987, 1997, and 1999 were when these three cartoon sitcoms first aired on television and they're still going! The SimpsonsSouth Park, and Family Guy are prime examples of how loyal fan-bases can truly be, even though they've been watching the same characters for two full decades (three for The Simpsons). At this rate, it honestly seems as though all three shows will go until the end of television as we know it.

RELATED: 10 Cartoon Network Shows That Ended Too Soon

Homer Simpson, Peter Griffin, and Eric Cartman have made themselves at home in our television sets, and the day any of them decide to move out will be a sad one at best, but they've still gone on long enough.

Perfect: Friends

Friends Joey interview Central Perk

Friends  is a show that portrays a time when your friends are your family. Creators David Crane and Marta Kauffman have undoubtedly said this thousands of times in the years since the NBC sitcom finally left the air back in 2004. It's the reason they've never wanted to do a reboot and it's the reason why the show ended at the perfect time.

Chandler and Monica had twins in the finale, Phoebe had gotten married to Mike, Ross and Rachel finally shipped-up, and Joey was set to get his own spin-off. The 'friends' now had their actual families, and while the sitcom's fan-base might've craved more, the decade cut-off truly did the Central Perk gang justice.

Dragged On: Grey's Anatomy

Bailey gives her interns the "5 rules" speech in Grey's Anatomy

There can't possibly be anymore anatomy left for Grey to examine! The show revolving around Dr. Meredith Grey and her colleagues at the Grey Sloan Memorial Hospital has been on the air for 15 seasons and is the longest-running prime-time medical drama ever. From the original cast, only four members remain and each of them has appeared in over 300 episodes.

RELATED: The Best TV Show Finales Of The Decade

The very hospital they work in has had two name changes since the beginning of the show, one of which was due to a plane crash. Please, Dr. Grey, it's time to pull the plug on this shows life support.

Perfect: Breaking Bad

Breaking Bad's Walter White

Argue all you want whether it's actually five or six seasons, it doesn't change the fact that every one of them was still a masterpiece. And the best part? It got out not only while it was still phenomenal, but while it was still believable. That may sound like a funny word to describe a show about a high-school chemistry teacher turned crystal-meth kingpin, but the truth that Breaking Bad revolved around was that Walter White's clock was ticking.

The genius method to span two years of events over a course of five (or six) seasons had every viewer still rooting for one of television's greatest antiheroes right up to the bitter, baby-blue end.

Dragged On: The Walking Dead

Seriously, we wouldn't have blamed you if you didn't know that the original Walking Dead show was still airing and producing episodes. Spanning to ten seasons, over 130 episodes, having a follow-up show where a host literally just talks about the show, and as of now, two spin-offs (one that has yet to air) this post-apocalyptic zombie narrative has suffered the same way as Grey's Anatomy in the fact that most of its original main characters have been killed off, thus leaving an empty shell of what the show used to be.

With so many other projects being done in this universe, it's conclusive to say that this particular Walker needs to meet its end.

NEXT: Closure: 5 Of The Best Series Finales (And 5 Of The Worst)