“Don’t think about pink elephants” – George Lakoff
This is something you probably have seen before, it’s called the Ironic Process theory. Tell someone to not think about something, and they will think about it. It is the basis of a lot of wrong behavior, like the “do not enter” sign on many doors, or the traffic sign telling you’re not allowed to drive down a certain road. Though it is often seen in small children (try to make them to not go somewhere) it is common in adults alike. And from it results a credo: if you don’t want someone to do something, make it impossible to do that, putting up a sign has contradictory effect, if the sign is read at all.
On the other hand, this theory could be of some use, from a marketing perspective for example. Apple is using this method widely in their marketing campaign, do not tell anything about your products and almost every tech magazine is talking about them, forbid users to jailbreak their iPhone and a lot of customers are trying.