Most important, is the user connection. The customer, especially the sophisticated customer, is a key participant in most successful experimenting processes. - Gustavo Duarte

http://duartes.org/gustavo/blog/post/Reality-Driven-Development

But software projects are not after "empirical reality", we just want working products. Built to Last deftly relates experiments to process in a chapter entitled "Try a Lot of Stuff and Keep What Works":