"Knowing or suspecting that we're being watched can stop us from engaging in certain kinds of behavior, even when it's perfectly lawful. For example, it might affect our decision to go to a certain barber (what would my other barber say?), meet up with a friend (what would my mom say?), eat at a restaurant (what would my trainer say?), or take the scenic route (is it suspicious that I'm not using my normal route?). Surveillance changes the way we make daily decisions—the same way that a rapidly approaching police car in your rearview mirror may make you feel nervous even when you are driving completely lawfully."