" In the struggle to cure syphilis in the first decade of the century, Paul Ehrlich concocted a drug, 606, that worked by poisoning Treponema pallidum, the spirochete that causes syphilis. It was called 606 because before it Ehrlich concocted 605 other drugs, none of which worked. Ehrlich, presumably, experienced 605 defeats but persisted. "

― Martin E.P. Seligman , The Optimistic Child