In the olden days, there were two sorts of people who traded stocks or bonds for a living. We can call them “dealers” and “investors,” though those terms are imperfect.1 An investor is someone who buys stocks or bonds because she thinks they are a good investment, and sells them when she thinks they aren’t. She does analysis, decides that Bond X is worth $80, sees it trading at $78, and goes out to buy some Bond X. When it trades up to $82, she sells it. She makes her money by buying low and sel...