Most people strive for a level of internal consistency. (To be the person we are at our core) We want our attitudes, beliefs, & behaviors to align with that. When our attitudes & behaviors clash we feel uncomfortable, which is known as cognitive dissonance.
We then often take steps to bring things back into alignment.
Here’s a crazy & great example:
In 1992 California was in a five-year drought and running out of water. In an effort to conserve water, the University of California Santa Cruz asked students to use less water several times. After not moving the needle some clever scientists decided to conduct an experiment!
This time instead of asking students to save more water, they simply asked them to sign a petition. A petition that just asked them to “recommend that other people save water”.
This team of scientists then intercepted several of the students at the gym and asked them to complete a survey solely about their own current behavior. (again not asking them directly to make any changes) By doing so they encourage the students to think twice about their efforts to best conserve water.
Next, the team timed how long each of these students took in the shower. (without being intrusive or making participants uncomfortable) The results found that the students who both filled out the initial petition “recommending that others save water”, & completed the survey at the gym (& perhaps recognized that they weren't saving water themselves) shortened their showers by over one full minute or 25% on average.
This suggests that by highlighting the gap, the team created a moment of cognitive dissonance within the students that lead to the desired behavioral change.