I voted undecided because, although I can observe the law of cause and effect, "believing" is not the word I would use about karma. It is obvious to me that one reaps what one sows. If I act unlovingly now, I also feel it now -- one could call this instant karma. And then, like Betrand Russell said, "In the part of the universe we know there is great injustice, and often the good suffer and often the wicked prosper, and one hardly knows which of those is the more annoying." The only way to understand such suffering is to consider karma. But, like I said, I don't "believe" in it -- but it does seem to explain the inexplicable.
Berynice