Grey's Anatomy premiered on ABC in 2004, and for the first few seasons, the series had a relatively small - or at least normal-sized - cast. Flash forward to today, the hit medical drama's main cast consists of so many characters that it seems even the writers and directors have a hard time keeping track.

Remembering names is one thing, but this show has way too many characters now and the ones that audiences actually care for tend to fall by the wayside in favor of giving screentime to insignificant characters such as new interns.

Having too many characters more often than not means having too many storylines, and this has been the case for Grey's Anatomy for several years. Many storylines and disregarded and left unresolved because they were forgotten or there was simply not enough time to wrap them up.

Let's explore the Grey's Anatomy graveyard for unresolved storylines and take a look at 10 of the most notable ones.

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LEAH MURPHY

Leah, Stephanie, and Jo looking confused on Grey's Anatomy

This has to be one of the strangest cases of an unresolved storyline on Grey's Anatomy. Leah Murphy was an intern in season nine, along with Heather, Jo, Stephanie, and Shane. This batch of interns were notoriously poorly developed and quite annoying, so of course Leah was no exception.

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Eventually, Richard decided to fire Leah because he deemed her not skilled enough to be a surgeon. This made her return in season 13 a rather puzzling one. And even more strange than that? The fact that after randomly resuming her career at Grey Sloan for a few episodes, Leah completely vanishes and is virtually never mentioned again.

IZZIE

Izzie Stevens was definitely one of the most impressively developed, widely beloved characters on Grey's Anatomy. She appeared for six seasons on the show, before Katherine Heigl's infamous feud with Shonda Rhimes put a sudden end to Izzie's medical career.

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There are so many things that Grey's never resolved about Izzie Stevens, and to this day, fans still have countless questions. Did her cancer ever return? Did she continue her career as a surgeon? Did she pick another profession in the medical field or discover a new passion altogether? Did she ever get married and have a family? We will most likely never get these long-anticipated answers, as the showrunners have firmly opted to leave Izzie's storyline unresolved.

MARK'S DAUGHTER

SLOAN RILEY GREYS ANATOMY

Sloan Riley became infamous virtually right from her introduction. She was vapid and unlikeable from the moment she moved in with Mark and Lexie, and her selfish personality eventually broke the couple up.

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After the baby and pregnancy drama, Sloane vanished from Grey's - never to be seen again - and was not even brought up after Mark's tragic death in season 9.

THE MEREDITH/MAGGIE/NATHAN LOVE-TRIANGLE

MEREDITH GREY MAGGIE PIERCE NATHAN RIGGS Greys Anatomy

Nathan was introduced in season 12, much to his brother-in-law Owen Hunt's contempt. Many fellow attendings and residents fell all over Nathan from the beginning, viewing him in the same light that many viewed "McDreamy" back in the day.

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Maggie and Nathan were both cardiac surgeons and began to get close. As Maggie started falling for Nathan, so did Meredith. Ultimately, Meredith and Nathan started their short-lived romance, Maggie and Meredith were at odds for a minute, and then all was forgotten as quickly as it occurred.

"DETH AND DIE"

SADIE HARRIS GREYS ANATOMY

Although the recent seasons of Grey's Anatomy have their share of unresolved storylines and forgotten characters, the early days were definitely no stranger to this trend either. The characters were more consistent back then, but some would vanish and become forgotten about just as easily as they are now.

A notable example of this was Melissa George's character, Sadie. Introduced in season five as an intern and Meredith's old college friend, the show immediately launched into the history of Deth and Die. Apparently, back in the day, Meredith and Sadie (aka Deth and Die) were quite the rebellious duo. All this aside, Sadie's gone almost as quickly as she appeared, and there's been virtually no mention of her ever since.

ERICA AND CALLIE

CALLIE TORRES ERICA HAHN Greys Anatomy

Brooke Shields' outspoken character, Erica, appeared as a guest star in the early seasons of Grey's, and eventually replaced Dr. Burke as Chief of Cardio in season 4. Callie and Erica's romance began when Erica started working at Seattle Grace, and being one of the first same-sex relationships to be portrayed on the show, it was quite a groundbreaking one.

But after being a series regular for a very short time, Brooke Shields was let go under some slightly shady circumstances and Erica was quickly erased and forgotten.

BAILEY'S OCD

An image of Miranda Bailey wearing her doctor's coat in Grey's Anatomy

Grey's Anatomy is no stranger to portraying characters with mental illness, and it usually does so in a very realistic, tasteful manner. The series had previously tackled afflictions such as PTSD, depression, and even schizophrenia, but their first stab at a portrayal of OCD was brought to life through Dr. Bailey.

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After an unfortunate and greatly traumatizing incident, Bailey develops severe OCD and becomes paranoid about washing her hands and keeping her ORs and herself completely germ-free. This goes on for quite a few episodes, in which Bailey suffers terribly, but then the show just kind of let's that storyline slip into the background until it is completely forgotten.

THE AFTERMATH OF THE PLANE CRASH

Meredith sitting among the wreckage of the plane crash on Grey's Anatomy

Many Grey's fans agree that the plane crash at the end of season 8 was one of the most tragic instances on the series, and the aftermath the most frustrating and infuriating. This is because there simply was no aftermath to this tragedy. Lexie and Mark were killed, Arizona lost her leg, Derek injured his hand, and Meredith and Cristina were left with severe PSTD.

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This kind of catastrophic event that brought on some heavy losses and changes requires some sort of an aftermath that should have been carried out through at least a few episodes, but early into season nine, a significant time-jump takes place, leaving the audience with no chance to grieve.

MEREDITH'S FERTILITY STRUGGLES

Derek flatters Meredith during her intern year in Grey's Anatomy

Meredith's struggle with fertility came to light after her marriage to Derek. Once the couple finally decided that they did indeed want children, they soon discovered that this was a virtually impossible task due to Meredith's "hostile uterus".

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The series makes a huge deal about this for quite some time. Then Meredith and Derek adopt Zola, and Meredith goes on to have two more children with basically no problems.

DR. DIXON

While the show was struggling to replace Erica Hahn, Seattle Grace went through a few attending heart surgeons, and Dr. Dixon was one of them. This character appeared in only a few episodes of Grey's Anatomy, but was unique and quite groundbreaking due to the fact that she was autistic.

Dr. Dixon would have been a very interesting character to keep around, but Grey's discarded her in absolutely no time, eventually replacing her with Dr. Teddy Altman.

NEXT: Grey's Anatomy: 10 Times The Show Broke Our Hearts