Paul Erdös on productivity

From wiki:

After 1971 he also took amphetamines, despite the concern of his friends, one of whom (Ron Graham) bet him $500 that he could not stop taking the drug for a month.[17] Erdős won the bet, but complained that during his abstinence, mathematics had been set back by a month: “Before, when I looked at a piece of blank paper my mind was filled with ideas. Now all I see is a blank piece of paper.” After he won the bet, he promptly resumed his amphetamine use.

H/T comments on Marginal Revolution.