What's the Scarcest Resource?

Surprisingly, the famous software/hardware designer and author, Dr. Fred Brooks, says that what holds up projects usually isn't money....

Brooks: The critical thing about the design process is to identify your scarcest resource. Despite what you may think, that very often is not money. For example, in a NASA moon shot, money is abundant but lightness is scarce; every ounce of weight requires tons of material below. On the design of a beach vacation home, the limitation may be your ocean-front footage. You have to make sure your whole team understands what scarce resource you’re optimizing. 

from a 2010 Wired Magazine article:    http://www.wired.com/magazine/2010/07/ff_fred_brooks/

He is called "the father of the IBM 360" (a major leap forward in computer hardware)

and author of The Mythical Man-Month:

You can’t accelerate a nine-month pregnancy by hiring nine pregnant women for a month. Likewise, says University of North Carolina computer scientist Fred Brooks, you can’t always speed up an overdue software project by adding more programmers; beyond a certain point, doing so increases delays.