Adding manpower to a late software project makes it
later
— a result of the fact that the expected advantage from
splitting development work among N
programmers is O(N) (that is, proportional
to N), but the complexity and
communications cost associated with coordinating and then merging their
work is O(N^2) (that is, proportional to
the square of N). The quote is from Fred
Brooks, a manager of IBM's OS/360 project and author of The
Mythical Man-Month (Addison-Wesley, 1975, ISBN 0-201-00650-2),
an excellent early book on software engineering. The myth in question has
been most tersely expressed as Programmer time is fungible
and Brooks established conclusively that it is not. Hackers have never
forgotten his advice (though it's not the whole story; see
bazaar); too often,
management still does. See also
creationism,
second-system effect, optimism.