Adam D'Angelo

You can go to Pinterest, and they'll get to know who your friends are, but they don't get to know very much about what you've done in the past. They're starting with little information about you, and they have to do this personalization.

By irreducibly complex I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning.