People’s tendency to comply more readily with a large request if they have already agreed to a smaller favor.
Example: According to this phenomenon, you should be more likely to convince your friend to make and decorate 200 cupcakes for the PTA bake sale in two days if you first ask for help with a smaller task, such as shopping for ingredients.
Grinnell, R. (2009). Foot-In-The-Door Phenomenon. Psych Central. Retrieved on November 28, 2015, from http://psychcentral.com/encyclopedia/2009/foot-in-the-door-phenomenon/