Why do people report on themselves?

Not long after I started using Twitter, I started to wonder: Why? Imagine the familiar movie scenario where a detective is desperate to track and find a suspect, or where a detective is hired by a suspicious spouse to trail their errant husband or wife. Or an alternate scenario from the Cold War, where the secret police manipulate ordinary citizens to inform on one another (cf. the film The Lives of Others , pictured at left). Or the horrible situation of a controlling husband who wants to know where his wife is at every minute of the day. In those situations, one person wants to track another; the person who is tracked would rather not be tracked and sometimes would do anything to avoid it. Now consider yourself, or any ordinary bourgeois, and how much you are tracked on a daily (and sometimes minute-to-minute) basis. Credit card companies and credit reporting firms register every purchase you make with something other than cash. Airlines, grocery stores and other businesses with rew...