"It always takes longer, it always costs more, it will always be harder, there will always be more, there will always be less than you expect, even when you take into account Hofstadter's Law."
Formulated as a stronger form of Hofstadter's eponymous law. It tries to put across the concept that no matter what you plan for something unexpected or unplanned for always occurs
First mentioned in Donald Norman's book "Turn Signals are the Facial Expressions of Automobiles".