The Buddha taught that because of karma, beings are bound to the ever-turning wheel of rebirth. Only when a person stops believing in the existence of a permanent and real self can he or she become free from karma.
Westerners often have trouble with this doctrine, for although they can easily believe that selfishness or ego-clinging causes suffering, it is harder to accept the existence of an invisible system of moral causality called karma. Likewise, since the dawn of the Christian era few Westerners have taken seriously the idea of many lifetimes, even though it was present in Pythagoras and some of Plato. And so we have Shakespeare's satire on Pythagoras in As You Like it, in which he has Viola sarcastically saying that she has not been entertained so much “since the time that I was an Irish rat, which I can hardly remember.”
The word “karma” literally means “action.” It is cognate with the most ordinary Sanskrit words for “to make” or “to do.” Many religious ceremonies are called “karmas,” which in this context simply means “ritual actions.” And there is the famous Hindu practice of seeking liberation through selfless work, which is called karmayoga—the yoga of activity.