Hofstatder's law: It always takes longer than you think, even after accounting for Hofstatder's law.

It always takes 10% more than the developer's estimate, even if he added 10%.

(I say 10%, but my estimates are usually 100% under, even if I added 100%)

It’s fun, but it’s not true. Some projects finish in time when planned with a large margin of safety.

In defense of Hofstadter's Law: it's about perception more than actual outcomes. And it doesn't predict infinite time. It can be converging to a limit, just that the limit is higher than expected.

The nice part is the recursion in the way this law is formulated.