How can anybody believe in karma???

[Butcho22]

Bad stuff happens to good people each and every day. I'm talking really, really bad. Rape, murder etc...

I would guess most christians believe that in the long run (possibly after death) good things will happen to those who do good. So they will say doing the right thing will "eventually" pay off.

But for those who aren't believers of God, how can you explain your belief of karma?