If you tell someone that they drive more recklessly because they have an airbag and seatbelt, they’ll loudly object. And they aren’t lying, per se: they definitely don’t perceive themselves as being less cautious just because they have those safety features. But ask them a different question: “If I disabled your airbag and seatbelt before you had to take a drive through busy traffic, would you be more careful?”
The point is this: Everyone behaves the way they do because of what they (consciously or unconsciously) perceive to be the costs & benefits, the risks & rewards, of doing so. They don’t always like knowing about it, but they do. Change the conditions, and you’ll change the behavior.
Knowing this formula, changes in behavior are easy to predict, even if people get really mad at you for predicting it. So hey, keep it to yourself – but act accordingly.
The Opportunity Machine 