@grimalkina some screenplays are jenga towers, where if you try to improve one bit -- a plot point or the motivation of a character, say -- it throws out another part. The problem is ridiculously overdetermined and you often can't tell if something will work unless you try it.
This is basically what people mean by 'development hell', where you end up making something different, not better.
@grimalkina A related problem is that once you've been working on something for multiple drafts, even the good parts bore you to tears, so you're tempted to start cutting or changing them, which causes even more problems. And you also become blind to completely obvious problems, like the fact that your protagonist is dislikeable. So you end up not solving problems that aren't the problem.
All of these can end up destroying your will to live!