Hofstadter's law

Hofstadter's law is a self-referential adage, coined by Douglas Hofstadter in his book Gödel, Escher, Bach: An Eternal Golden Braid (1979) to describe the widely experienced difficulty of accurately estimating the time it will take to complete tasks of substantial complexity:

"Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law."

The law is often cited by programmers in discussions of techniques to improve productivity, such as The Mythical Man-Month or extreme programming.

History
In 1979, Hofstadter introduced the law in connection with a discussion of chess-playing computers, which at the time were continually being beaten by top-level human players, despite outpacing humans in depth of analysis. Hofstadter wrote:

"In the early days of computer chess, people used to estimate that it would be ten years until a computer (or program) was world champion. But after ten years had passed, it seemed that the day a computer would become world champion was still more than ten years away... This is just one more piece of evidence for the rather recursive Hofstadter's Law."

In 1997, the chess computer Deep Blue became the first to beat a human champion by defeating Garry Kasparov.