Streetlight Effect
Drunkard's Search
The tendency to search for answers only where it's easiest to look, rather than where they're most likely to be found. Named after the joke about a man looking for lost keys under a streetlight because "that's where the light is."
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Origin
The underlying joke traces back to Nasreddin Hodja, a 13th-century Sufi folklore figure. It entered the social sciences in 1964 when Abraham Kaplan coined "the principle of the drunkard's search" in The Conduct of Inquiry. The full joke: a policeman finds a drunk searching under a streetlight and helps him look. After a few minutes he asks, "Are you sure you lost your keys here?" The drunk says no — he lost them in the park. "Then why search here?" "Because this is where the light is."
Updated February 22, 2026