How we change what others think, feel, believe and do
Minimal Justification Principle
When someone does something and there is minimal justification for them doing it, this creates more dissonance than if they can explain it through a significant rationale. The dissonance then acts to make them internally justify the action, saying 'I wanted to do it anyway because I like doing that sort of thing.'
Festinger said it in 1957 "if one wanted to obtain private change in addition to mere public compliance, the best way to do this would be to offer just enough reward or punishment to elicit compliance."
Festinger and Carlsmith (1959) gave people a boring job then ask the participant to do a favor in 'recruiting' a woman in the waiting room by telling her how enjoyable the task was. Some were offered $1 to do this and others were offered $20. Afterwards they were quizzed as to what they felt about the boring task. Those who received $20 said that they really thought the task was boring while those who received only $1 stated that they really believed the task was enjoyable.
The explanation is that doing something in which they do not believe a person does not believe in for a minimal reward sets up more dissonance than doing that same thing for a larger reward.
When you are asked to sign a petition in the street, you justify it to yourself by saying you really do support the cause. You are then more likely to give money, volunteer, etc.
Give people small rewards for the things you want them to keep doing. Even praise is often enough. Beware of big bonuses and other major rewards that get only compliance.
Beware of people giving you small rewards. Watch how you feel about them. Think hard about what the other person gets from it all.