This is a lesson that never gets driven home hard enough: I have no idea of the depth of other people's pain.
Sometimes I run across that quote from Plato: "Be kind, for everyone you meet is fighting a hard battle," but somehow that quote just rubs me the wrong way. It makes it sound like other people have financial difficulties or an upcoming round in the gladiator ring and that I have the extra burden of kindness because of it; I wish the quote said, "Other people's heartaches are often bigger than yours."
Because it's not financial difficulties or career choices that are plaguing people. Sometimes your boss is going through a divorce and doesn't exactly want to talk to you about it. But if you knew that, wouldn't you have a little more patience for her bad mood?
And even the word divorce isn't strong enough, sometimes, to bring out the compassion. What I really mean is that sometimes your boss is throwing in the towel on a fight that's lasted two years now and her whole family is splitting up and her kids are miserable and crying a lot and this is her husband, the man who stayed up all night with her when she was writing her thesis just to keep her company and nobody did anything wrong but they can't work it out and she finds herself saying hateful things to the people she loves best. So if she's a bit snippy with you in a meeting about something you've been meeting about for months, it probably has nothing to do with you.
And sometimes the reason your friends do confusing things is because they're confused. Sometimes your friend's father is dying and not only does she sort of wish he'd hurry up and do it because watching someone waste away at a hospital every night is not only painful but intrusive, but she's feeling guilty for feeling that way and doesn't think you would understand, and then her relationship with him was pretty complicated anyway because he really wasn't around that much, they never really talked about important things, and this is her last chance to spend time with him but they still just sit around discussing television shows and how can she start having a real conversation with him? So when she doesn't really want to talk about what's going on in her life but does really want to go to Mill Avenue on a Friday night, it might have nothing to do with you.
Point being, other people have wounds you aren't aware of, and sometimes wounds they won't ever reveal. Sometimes your relationship is their Band-Aid and they don't want you to know that, or admit it to themselves. Sometimes your relationship is lemon juice in their paper cuts and they are loathe to say so.
I think if I could have one wish granted, it would be always to be aware of these sore spots, even if I can't know the details. I don't want to blindly go around being compassionate to other people in case they happen to be in pain; I have trouble putting sweeping abstract principles like that into action. But I wish I had better radar for it.