Loss aversion

“The disutility of giving up an object is greater than the utility associated with acquiring it”.

People are loathe to give up what they already possess. If you can get people to buy in, even a little bit, to your product or service, then you’re way ahead of the game. When you threaten to take away their free trial, their position on your mailing list, or their access to resources that you gave them, they intensify their desire, and therefore their commitment to your product or service.