Predictably irrational
We go apeshit at the mention of "free stuff". "No" doesn't necessarily mean "no" when we're horny. You will shop around for cheap cigarettes, but not for an expensive suit. Economics is dead wrong. And many other interesting findings.
We all have our theories about humanity and how we people operate. But our theories are irrelevant without actual data to compare them to. Now we've got some, very briefly explained in this highly recommended outline of the book.