As posted by Bill at Integral Options Cafe, this was worth a repost because it's so clear, so logical, and so empirical.
Today's Rigpa Glimpse of the Day:
Is karma really so hard to see in operation? Don’t we only have to look back at our own lives to see clearly the consequences of some of our actions? When we upset or hurt someone, didn’t it rebound on us? Were we not left with a bitter and dark memory, and the shadows of self-disgust? That memory and those shadows are karma. Our habits and our fears too are also due to karma, the results of our past actions, words, and thoughts. If we examine our actions, and become really mindful of them, we will see that there is a pattern that repeats itself. Whenever we act negatively, it leads to pain and suffering; whenever we act positively, it eventually results in happiness. ~ Sogyal Rinpoche