From Clay Shirky's In Praise of Evolvable Systems

Only solutions that produce partial results when partially implemented can succeed.

Sometimes you have to make up the partial results, but producing them is essential. They have to be real goals, not just "Ok, I did this now" milestones. The space program of the 1960s is a good example. The diversity of and number of systems built to accomplish the very indivisible goal of "man on moon" was enormous.