I’ve noticed that TV shows fall on a spectrum of redemption. At the start of each series, the show runners seem to establish a clear point of “redeemability” for the characters. And that quality remains fairly consistent throughout the run.
For example, the characters on Seinfeld are completely incapable of self-improvement. Nobody ever seems to learn from their mistakes. The comedy comes from the endless loop of self-absorbed narcissism that the four main characters share.
At quite a different point in the spectrum is The Big Bang Theory. The characters are very flawed, it is true, but they are, for the most part, quite capable of growth and redemption. Even Sheldon.
Compare, for example, the final episodes of those two shows. Each is, in a sense, a summing up of everything that came before.
The punchline at the very last episode of Seinfeld is that these characters are completely hopeless, and utterly incapable of doing better. The message at the very last episode of The Big Bang Theory is precisely the opposite.
In both cases, we are not surprised. We have been prepared for years for those respective endings from the very beginning.
Of course this spectrum forms a continuum. Frasier, for example, seems to fall exactly in the middle.