Even more so than movies, TV shows are built on their casts. Iconic small-screen characters have carried entire shows into the realm of superstardom, and the ever evolving will-they-won't-they drama of potential romances have captured the attention of audiences over the span of years, maybe even decades in the case of certain shows.
However, while the sense of familiarity and connection to amazing characters that comes with long-form TV storytelling is special, it's not easy to maintain. Whether it's writers running out of ideas or actors getting bored of playing the same character for so long, sometimes characters don't fulfil their potential, or end up disappearing entirely.
Sometimes that's not a bad thing, and it can result in a great send-off for fictional friends and enemies audiences have become attached to, but other times they're unceremoniously cut out, there one episode and gone the next, leaving viewers wondering what the hell happened.