Well, it's a matter of degree. Like, accepting the fact that the later parts of a series suck, but still appreciating the earlier, good parts as their own thing. It's adjusting the mental boundary between jumping the shark and retroactive ruination. Like, if the first two seasons of a TV show are good, and the third is not, I tell myself to be happy with the first two seasons and pretend the third doesn't exist.

It's kind of like the difference between thinking a book is actively bad, and acknowledging that I don't like it just because it's not the book I wanted it to be, but further down the suck scale.

Some things go so bad that it's impossible to do that, in which case avoidance is the only possible course of action.