How we change what others think, feel, believe and do
Commitment devices are tricks played on oneself or other people in order to increase commitment to some action, belief, etc. This can be as creative and extreme as needed -- the only measure is whether the method is successful.
A classic technique is to make commitment or not visible in some way, for example putting a graph of you weight or the number of bottles of wine consumed on the wall.
Another method is to make your commitment public, so you will be embarrassed if you break the commitment. Asking others to check up on you is a similar principle.
Leavitt and Dubner (2007) give the rather gross example of a Los Angeles slimmer who bought lifelike plastic models of human body fat from a medical-supply company and put them on display in her kitchen.
'Mutually Assured Destruction' (MAD) is a commitment device that has prevented nuclear war, as any nuclear power knows that to attack another is to also suffer devastating attack. The principle also applies in less significant settings.
There are many times we want to do something but we fail to do so, from losing weight to completing college assignments on time. We easily forget, procrastinate or otherwise find excuses not to stick to commitments. Commitment devices are methods to help us stick to the commitments we have made, even if they are just to ourselves.
The basic principle of a commitment device is to make failure to stick to the commitment more painful than remaining committed. This can use aspects of both punishment and reward, although the former is more common.
Another principle that may be used is of consistency, where a person will change beliefs in order to sustain consistency with actions. If you can get them to do something, they then change beliefs to 'It is normal and right for me to do this thing' and so create self-sustaining behavior.
Commitment devices can be used when getting others to stick to a promise of some kind. Formally, we can use contracts that may or may not be legally binding (but which in any case increase the commitment felt).
Criminals build commitment in those they coerce with devices that include severe punishment, from kneecapping to assaults on your family.
Commitment devices do not always work -- the many slimming aids on the market coupled with the many overweight people indicate this. Similarly, there are many who have used various devices to unsuccessfully try to stop smoking.
Leavitt, S.D. and Dubner, S.J. (2007). Freakonomics, Penguin Books