This translation captures the meaning and beauty of the twelve principal Upanishads, omitting a few passages. Original text is not given. An excellent version for the general reader.
Desire, want, is the father of all misery. Desires are bound by the laws of success and failure. Desires must bring misery. The great secret of true success, of true happiness, is this: the person who asks for no return, the perfectly unselfish person, is the most successful.
-Swami Vivekananda