The Commitment and Consistency principle is one of the six principles established by Cialdini (1984) in his book Influence: The Psychology of Persuasion. It describes the way in which people want their beliefs and behaviours to be consistent with their values and self-image. Firstly, we tend to view consistency as an attractive social trait and as indicative of someone being rational, trustworthy and stable, and so we all want to be seen to be consistent. Secondly, the Commitment and Consistency principle is a mental shortcut we use to simplify our decision-making: we are given so many decisions to make daily that we reduce this amount by using a past decision as reference for subsequent related choices. The consequence of this cognitive bias is that we act in ways that are consistent with our initial action or thought, so that when we commit to something or someone, we stick to it. We also try to behave in ways that are consistent with the image we have portrayed to others, and with the public image they have of us.

For example, if an individual is thought of as someone who knows about politics, he or she is more likely to participate in subsequent political conversations, even if they have no real interests but simply want to remain consistent with this public perception of their character. In the same way, children who are often congratulated by their parents for achievements and working hard are more likely to continue to work hard and do well in order to remain consistent with this external perception of themselves.

The Commitment and Consistency principle has many applications in marketing strategies. Encouraging customers to make a small commitment to your brand or site (by offering them something easy to complete and/or free - perhaps a free trial or simply signing up for membership in order to get a discount) you are then in a better position to motivate them to continue on engaging with your site as they will feel compelled to remain consistent with this initial behaviour.