Dictionary.net

"Adding manpower to a late software projectmakes it later" - a result of the fact that the expectedadvantage from splitting work among N programmers is O(N) (that is, proportional to N), but the complexity andcommunications cost associated with coordinating and thenmerging their work is O(N^2) (that is, proportional to thesquare of N).The quote is from Fred Brooks, a manager of IBM's OS/360project and author of "The Mythical Man-Month".The myth in question has been most tersely expressed as"Programmer time is fungible" and Brooks establishedconclusively that it is not. Hackers have never forgotten hisadvice; too often, management still does.See also creationism, second-system effect, optimism.