People don't like to be pushed into a corner, even if you're making the simplest request. A recent study suggests that if you want people to be more compliant, you need to give them a better sense of freedom in the matter. Photo by Daniel Steuri.
The study, led by Nicolas Guéguen, and published in the Polish Psychological Bulletin, suggests that phrasing requests a certain way can make people more likely to comply with them. In the study, people were more likely to donate money when the phrase "You'll probably refuse, but..." was used. According to Guéguen, beginning requests with phrases like that one or something similar -- "You don't have to, but..." -- gives people a sense of freedom when it comes to saying yes or no.
Basically, you give them an out -- the freedom to choose not to do something. Whatever they choose is now their idea, not a restrictive request you've forced upon them. Because your request puts them into consideration, they're more likely to help you out.
"You will probably refuse, but…": When activating reactance in a single sentence increases compliance with a request [Polish Psychological Bulletin via Science of Us]