A good illustration from today's session of my Criminal Law class, which was the first law school class these students ever had. I passed around a seating chart, and asked students to write their first names, last names, and any pronunciation key for their names. At the end of the class, I got the chart, and nearly every student included a phone number.

Why?, I thought. I didn't think I said anything that could have been misheard as a phone number.

And then I realized what must have happened: The first student included a phone number, for whatever individual reason (perhaps because the student thought it would be helpful, or because this was asked in some classes at the university the student went to before). Then the next student saw this, assumed a phone number was requested (relying on the first student's judgment rather than his own memory of what I asked). And once the first few boxes had phone numbers as well as names, the path was set: Nearly everyone else followed suit.

Had the first student not included the phone number, I'm pretty sure this wouldn't have happened; likewise if this hadn't been the first class the students had. (I wonder, by the way, whether people will do the same in other classes. I expressed some surprise at seeing the phone numbers after class, but not loudly, so only a few students heard it.) But this one person's decision led the rest of the students, quite rationally, to do what they saw others doing.