Why are group decisions so hard?

Since the beginning of human history, people have made decisions in groups--first in families and villages, and now as part of companies, governments, school boards, religious organizations, or any one of countless other groups. And having more than one person to help decide is good because the group benefits from the collective knowledge of all of its members, and this results in better decisions. Right?

Back to reality. We've all been involved in group decisions--and they're hard. And they often turn out badly. Why? Many blame bad...