I’ve read several different implementations of this idea recently, the most recent in Bruce Schneier’s assessment of different IT security systems, but in a wide variety of contexts the core idea is true, and very powerful:

Years ago, Bill Joy, one of the founders of Sun Microsystems, made a statement that is still true today—that no matter what your company is, most of the smart people in the world work somewhere else. Open source is a way of leveraging those untapped resources—those smart people.

This iteration from Mitch Kapor.