From the back cover of Thomas C. Schelling’s Micromotives and Macrobehavior, a book that Håkan recommended recently:
Through familiar and readily grasped examples, [the writer] demonstrates what happens when behavior in the aggregate is more than a simple summation of individual behaviors [emphasis mine], how members of a society tend to be blind to the collective consequences of their separate decisions, and why attempts to infer individual intentions from group phenomena are tricky at best and often downright impossible.