The adage that a task will always take longer than expected, even when Hofstadter's law is taken into account. The law is therefore endlessly recursive. Although often taken facetiously, the law makes the serious point that something unexpected is very likely to occur in the completion of any complex task, no matter how carefully one plans. It is therefore a good antidote to planning fallacy and optimism bias. The law is named after the US academic Douglas Hofstadter (1945– ).