Fitzgerald, in the beginning of The Crack-Up (a beautiful book available on the site of Esquire, where it was first published)

“Before I go on with this short history, let me make a general observation—the test of a first-rate intelligence is the ability to hold two opposed ideas in the mind at the same time, and still retain the ability to function. One should, for example, be able to see that things are hopeless and yet be determined to make them otherwise”