… too tight a schedule will inevitably lead to the temptation to take shortcuts. These shortcuts might succeed in getting the system working on time – but only if everything goes right, which it rarely does.
Gerald Weinberg The Psychology of Computer Programming Silver Anniversary Edition p68
The Psychology of Computer Programming was originally published in 1971 but remains a great read and very relevant even in a very different computing world. I have the silver anniversary edition which reprints the original with additional commentary at the end of each chapter – what Weinberg calls “wisdom of hindsight remarks”. Weinberg’s comments – 25 years on – about the above quote state:
The wisdom of age has made me ashamed of this statement. “Rarely” is pussy footing; something always goes wrong. Shilly-shallying like this by authors like me has perpetuated the myth of the “optimistic” estimate – how long a project would take if everything went right. Such “estimating” might just as well be based on the assumption that the Laws of Thermodynamics will be repealed during the project.
Gerald Weinberg The Psychology of Computer Programming Silver Anniversary Edition 5.i