As it is written in "The Tao Of Programming"( http://www.canonical.org/~kragen/tao-of-programming.html ):

A manager went to the master programmer and showed him the requirements document for a new application. The manager asked the master: ``How long will it take to design this system if I assign five programmers to it?''

``It will take one year,'' said the master promptly.

``But we need this system immediately or even sooner! How long will it take if I assign ten programmers to it?''

The master programmer frowned. ``In that case, it will take two years.''

``And what if I assign a hundred programmers to it?''

The master programmer shrugged. ``Then the design will never be completed,'' he said.