Some time ago I was following a behavioral research project being carried out on the subject of motivation. The underlying concept had more to do with how to get people to do things than why they do them. Along the way some interesting things were learned about both aspects of motivation. In any case, the basic flow of the experiment involved cutting in line.
A researcher would come up to people who were waiting to use a photocopier, and ask to cut in, "I only have a few pages, may I go first because I am in a hurry?" Something like 90% of the time, the person asked would let them in front. In another case they would come up to someone waiting to use the photocopier and ask to cut in, "I only have a few pages, may I go first?" To this approach only something like 60% of people let the researchers go first.
The intial thinking was that it was the "I am in a hurry" that prompted the different reactions. They then adjusted the experiment to include other fake "reasons", including some very poor ones like "because I have to make copies". It was quickly apparent that giving a reason always prompted more success than without. Much more success.
Simply including a "because" with their request created a dramatic increase in the percentage of success for the request being granted. This simple exercise demonstrated (albeit indirectly) how important having a justification can be for actions.
As individuals we love to have reasons for things, it makes us feel secure. When you are given a reason for something, your brain can go "Alright then, as long as there’s a reason!". People love reasons, so if you are in a position of trying to influence someone, just give them one.
Of course, it should be obvious that if the likelihood of someone complying with a request is zero, then increasing it by any percentage (even a large one!) is still going to be zero. For example, I have well publicized that I am willing to give Sarah Alexander one of my famous back-rubs for no charge, because they’re very relaxing. However, the chances of that happening are pretty close to zero and I have yet to hear from her. Sarah, if you’re reading this, the offer is still very much on the table.