Cognitive dissonance is an unpleasant state that occurs when we notice
discrepancies between our
attitudes or between our attitudes and
behaviour.
Dissonance often occurs in situations involving induced compliance - ones in which we are induced by external factors to say or do things that are inconsistent with our true attitudes.
In such situations, attitude change is maximum when we have reasons that are barely sufficient to get us to engage in attitude-discrepant behaviour. Stronger reasons (or larger rewards) produce less attitude change - the less leads to more effect.
Inducing individuals to advocate certain attitudes or behaviours and then reminding them of their hypocrisy - the fact that they haven't always behaved in ways consistent with those views - can be a powerful tool for inducing dissonance and thus promoting benificial changes in behaviour.
Dissonance appears to be a universal aspect of social thought, but the conditions under which it occurs and the tactics individuals choose to reduce it appear to be influenced by cultural factors.