Anyone who's spent much time in the classroom as an educator has inevitably seen the phenomenon of students packing up their materials prematurely. A couple weeks ago, I was showing a documentary in class, and like clockwork, someone started packing up with five minutes left in class. This, of course, prompted several others to start packing up. The sound of one person rustling with her belongings is largely ignorable, but several people messing with their stuff is distracting. It occurred to me that this is actually a good example of the social generally. One individual's behavior is inconsequential, but patterned collective behavior has ramifications. For example, if one person opts not to vote, it won't change the election; if many people don't vote, it has a measurable effect on the outcome. If one person drives an SUV, no problem; if many people drive SUV's, it accelerates global warming and increases the rate of fatalities.