No good deed...

I hate to sound negative...but sometimes it seems no good deed goes unpunished. I REALLY try to be a good friend. I listen to others- I do things with them when it's the right thing to do (even if i dont want to)...blah blah blah...but why do some people just turn out to be shitty? I had a friend tonight get mad at me for I swear to you I have no idea what...if you paid me to tell you why he got mad I couldnt do it...I know he's going thru a really really bad spell and I try and be understanding- but how far can friendship go??