Hofstadter’s law

Hofstadter’s law states: it always takes longer than you expect, even when you take into account Hofstadter’s law. It was coined by the cognitive scientist Douglas Hofstadter in his 1979 book Gödel, Escher, Bach: An Eternal Golden Braid, where he used it to describe the recursive difficulty of estimating how long a complex, self-referential problem will take to solve.

The law is deliberately self-defeating: knowing that estimates are systematically optimistic does not, in practice, fix them, because the same psychological and structural forces that produced the original underestimate also bias any adjustment made to correct for it. Padding an estimate to account for the historical tendency to run over time is itself a new estimate subject to the same bias.

In software development the law is invoked constantly around scheduling and project estimation, where it captures the same lived experience as the ninety-ninety rule and Parkinson’s law. It is one of the most quoted laws in the folklore of software estimation precisely because attempts to outsmart it, by padding, by planning poker, by historical velocity data, tend to run into the same recursive problem it describes.

See also

• Laws and principles

References

• Hofstadter, Douglas (1979). Gödel, Escher, Bach: An Eternal Golden Braid. Basic Books.