If we listened to our intellect, we'd never have a love affair. We'd never have a friendship. We'd never go into business, because we'd be cynical. Well, that's nonsense. You've got to jump off cliffs all the time and build your wings on the way down.
Source: In The Ultimate Success Quotations Library, 1997.
-- Ray Bradbury, (Aug 22 1920-2012), US science-fiction writer; He is best known for SF stories combining social criticism, e.g., Fahrenheit 451 and The Martian Chronicles.