I find it comes naturally to me and that makes it difficult for me to define "how do you learn it".
For me it's a Nike kind of thing, "just do it"..
Some of the deepest arguments we've had around here were because of this exact issue.
I find in myself that it's impossible for me not to be happy when someone else is happy. Even if something horrible is going on, in the moment I'm considering their happiness, I'm happy.
"Love As Thou Wilt"