The second kind of problem is what’s usually called a coordination problem. Coordination problems require members of a group (market, subway riders, college students looking for a party) to figure out how to coordinate their behavior with each other, knowing that everyone else is trying to do the same.
Diversity and independence are important because the best collective decisions are the product of disagreement and contest, not consensus or compromise.
The market was smart that day because it satisfied the four conditions that characterize wise crowds: diversity of opinion (each person should have some private information, even if it’s just an eccentric interpretation of the known facts), independence (people’s opinions are not determined by the opinions of those around them), decentralization (people are able to specialize and draw on local knowledge), and aggregation (some mechanism exists for turning private judgments into a collective decision).
With most things, the average is mediocrity. With decision making, it’s often excellence. You could say it’s as if we’ve been programmed to be collectively smart.