Fascinating little piece (sub reqd) in New Scientist on the inclination we sometimes have to do the exact opposite of what someone wants us to do (like the teenage girl who deliberately goes out with the boy her parents have warned her to stay away from). Rather than being just plain contrariness this is actually a recognised psychological state called Reactance, first described by Jack Brehm, a social psycologist at the University of Kansas – the theory that "when someone perceives a threat to their freedom of action, they become motivated to re-establish that freedom".
Experiments have shown that reactance can happen subconsciously, supporting the idea that it is an evolved response to help us maintain our freedom to make our own decisions. One experiment, by Duke University North Carolina, asked people to write down the names of someone in their lives who they felt was controlling and wanted them to work hard. Even a subliminal flash of the name made their volunteers perform worse on a word task as they reacted subconsciously to what they thought that person wanted them to do.
Perhaps unsurpisingly young people are more susceptible than old, men more than women, and people are more likely to rebel against rules they perceive as unfair. But the New Scientist uses the example of how advertising with a strong anti-alcohol message can actually prompt students to drink more beer, in order to show how strong the reactance drive can be.