Many slash fans are so attached to their OTP that they can't bear to read a story that doesn't end with the pairing happily together. Some fans make their friends pre-read stories for them (see Merry-safe ending). Others mentally speedbump any unhappy ending they read. In other words, they basically ignore the unhappy ending the author has carefully put at the end of her story, and mentally paste on a happier ending after it.
Here's an explanation from 1997:
Say that story ends with one of them walking out the door...leaving."No!," you cry. You put down the zine, take a deep breath, and think, "He'll be back. Heck, he'll be back tomorrow, with a hangover--No, he'll be back tonight, drunk and sorry. No, he'll be back in minutes; by the time he makes it down to his car, he'll be regretting the whole thing!" You've completely re-written the end of the story: that's turning their
original ending into 'just a speedbump' for the characters to drive over on their way to a happy ending.
- ↑ [post by Sandy Herrold to Virgule-L, Fri, 21 Feb 1997]