Robert A. Heinlein: Love
Love is that condition in which the happiness of another person is essential to your own.
Robert Anson Heinlein (July 7, 1907 – May 8, 1988) was an American science-fiction writer. Often called the "dean of science fiction writers", he was an influential and controversial author of the genre in his time.
Heinlein became one of the first science-fiction writers to break into mainstream magazines such as The Saturday Evening Post in the late 1940s. He was one of the best-selling science-fiction novelists for many decades.