Empathy is imagining what it feels like to be somebody else.
When we introduce children to this idea, it’s usually because one of them snatched a toy away from another one. We point out to the toy thief that she wouldn’t like it very much if someone came along and stole her toy. Then we explain that other children have feelings just like hers. The lesson is: Treat other people the way you want them to treat you.
If you’ve been out of kindergarten for a while, you may have noticed that not everyone likes the same things you like. There’s some overlap (nobody likes having their toys stolen), but people can have very different ideas about what it means to be treated well.
Empathy isn’t really about how you would feel if you were treated a certain way. It’s about how someone else actually does feel when treated that way. This can be a tricky distinction, even for adults. I’ll give you an example.
Say you have a friend who is very tall. He is so tall that complete strangers often announce to him that he is tall and demand to know his exact height. He says it’s sort of annoying, but you don’t believe him because you’ve always been self-conscious about your own height. You are short. You’d love it if you were so tall that people stopped you on the street to talk to you about it. You can’t imagine how this could ever annoy anyone.
But if you want to empathize with your friend, it doesn’t matter how you think you’d feel if you suddenly became a much taller person. You have to imagine being your friend, seeing things the way he does, surrounded constantly by tiny irritating people who won’t shut up about his height.