A character loses so much in pursuit of their goals that we're left with the depressing understanding that it probably wasn't worth it

Thanos - Avengers: Infinity War. One of the most well-known examples in recent years and somewhat self-explanatory.

Andrew Nieman - Whiplash. He's finally earned the abusive Fletcher's respect, but at this point he's been expelled, broken up with his girlfriend, alienated everyone close to him and has become a very troubled person in his pursuit of greatness. Damien Chazelle (the director) straight-up stated in an interview that Andrew will probably die in his 30s from a drug overdose.

Ellie Williams - The Last of Us Part 2. One of the major reasons, from what I've gleaned, as to why the game's story remains fiercely debated to this day and arguably an example of this trope done poorly. The messages of "revenge doesn't solve anything" and "the cycle of violence will never end until someone decides to just stop" are sound ones, but Ellie ultimately giving up her quest for revenge at the literal last minute means that the story ends with her having lost everyone close to her, and even her ability to ever play the guitar again - one of her last connections to Joel. So, if anything, her journey concludes with her circumstances even worse than when she started.