But what happens when we make those obstacles too hard for the reader to get past them? Sometimes the line gets blurred between one of the characters going almost to the edge and when they have actually gone over the edge into hell.
I unknowingly took my characters too close to that edge in one of the first few stories I wrote. The editor didn't find it too close, nor did I. But after reading a particularly scathing review I realized that I actually agreed with the reviewer (who hated the story because one character's transgressions were too great to be forgiven). I can tell you that I never made that mistake again. You can write yourself into a hole as long as you can make your characters legitimately and believably crawl out of that hole.
Ultimately, the line between what's forgivable and what is not is eye of the reader, although some things are never okay to forgive -- physical abuse, for example. But where is your line? And have you ever read a book that allowed the characters to cross that line? Did you hate the book? Curse the author? I want to know.