A police officer sees a drunken man intently searching the ground near a lamppost and asks him what he is looking for. The man replies that he is looking for his car keys, and the officer helps for a few minutes without success. Then the police officer asks the man whether he is certain he dropped the keys near the lamppost. ‘No,’ comes the reply, ‘I lost the keys somewhere across the street’. ‘Why look here then?’ asks the surprised and irritated officer. ‘The light is much better here,’ the intoxicated man responds as if stating the obvious.
Abraham Kaplan, the first philosopher to examine behavioral sciences systematically, referred to this as ‘the principle of the drunkard's search’, a type of observational bias that occurs when people search for something only where it is easiest to look.