Makes me think of the comparisons people are constantly performing.  If you see someone else exert self-control, you can do so while your inherent cognitive comparison functions deduce that in doing so you are not "doing worse" than the other person; you are not missing out on something that they are getting.<p>Also, in comparing, you may see the abstention of the other person as advantageous.  For example, if weight gain is a consideration, that other person's abstention helps them to control their weight and -- at least by current, U.S. society's evaluation -- improve their appearance.  You may then be motivated to do the same, so as to not compare poorly to them in terms of physical appearance.<p>Further, I'd argue that what's in front of you has the most immediacy.  When you directly confront these situations, they have a stronger influence than when you have knowledge of them but are currently separate and alone.  Advertising may overcome this in part by saturation.  If the saturation is sufficient, then furthermore, you are never far from its immediate, real-time influence.