The foot-in-the-door technique is the idea that it is more effective to start by asking people for something small, and then when they give it to you, you are in a better position to ask for something bigger. Indeed, Freedman and Fraser (1966) have shown that a small agreement creates a bond between the requester and the requestee. The person you ask acts according to the cognitive bias that they have to justify their agreement to themselves. Humans like to justify their decision-making so they will convince themselves that they accepted the first request for a reason and then feel obliged to act consistently with this reason by accepting a second and third request, and so on. The phrase “foot in the door” originated during the heyday of door-to-door salespersons that would place their foot in the way of a closing door. With their foot literally in the door, the potential customer would have to listen to the sales pitch and this would potentially give them their way in to a bigger sale.

Freedman and Fraser conducted many studies that demonstrated this cognitive bias. In one of them, they asked people to place either a small sign in their car window to promote safe driving, or a small sign in a window of their house about keeping California clean. About two weeks later, the same people were asked by a second person to put a large sign advocating safe driving or “keeping California clean” in their front garden. Many people who agreed to the first request also complied with the second, far more intrusive request.

Foot-in-the-door technique also works online for web marketing strategies. For example, you can ask for an email address (a small request that doesn’t cost anything or take too much time) and once the user has given this, they’re then much more likely to agree to complete a bigger, more important task (register online, sign up for a newsletter, make a purchase etc.).