I have always understood empathy as “feeling what someone else is feeling”. It is a capacity given to the more emotionally permeable among us. I’ve felt this, and I’ve also imagined I felt it when I was just imagining myself in their situation and having an emotion. It takes some experience, humility, and boundary discipline to differentiate these two.
I used to think I was special for being able to feel what someone else is feeling but now I am wary and old, distrust my own conclusions, and in general try to avoid the whole thing, as it is draining and often quite painful.
Sympathy is quite different than feeling what someone else is feeling. It is external to the object, and can be synonymous with pity, which easily becomes sentimentality or condescension. It can also foster a false sense of identity with the object (“we feel the same way, we are brothers”).
Sociopaths don’t feel either one. They may be able to figure out how to manipulate people for their own ends but they lack the capacity to realize that other people are just as valuable as they are.
As for literature, I think it makes you a much keener observer of human nature. Must agree with Tolstoy being the master. What you do with those observations is up to you, but at least you have increased your capacity to see what is there, which is the basis of healthy human interactions.