Every action we perform leaves an imprint, or potential, on our very subtle mind, and each karmic potential eventually gives rise to its own effect. Our mind is like a field, and performing actions is like sowing seeds in that field. Positive, or virtuous actions sow the seeds of future happiness, and negative or non-virtuous actions sow the seeds of future suffering. This definite relationship between actions and their effects - virtue causing happiness and non-virtue causing suffering - is known as the law of karma. An understanding of the law of karma is the basis of Buddhist morality.
—Geshe Kelsang Gyatso - “Eight Steps to Happiness” (via dancingdakini)