The greatest lesson you've learned from classical fiction?

I am currently enjoying a very thought-provoking semester of American Literature. Prior to this class, I wouldn't have considered fiction as useful in my everyday life, as opposed to something like a self-help book. What I've found is exactly the opposite, and I have found novels such as Great Expectations to be even more influential than anything I've ever read.

So I ask you all, what is the greatest lesson you've learned from classical fiction?