I read an article somewhere that they researched asking people to cut in line, giving various reasons.
No reason, "Can I cut in front of you?" failed most of the time.
Any reason, doesn't matter what- "Can I cut in front of you because my brother loves to snow ski" and the percentage went way up, it made little difference what the reason was. This is an interesting tidbit about human nature.
Not very surprising; many studies have also shown that employees are more likely to follow management directives when they are given a reason. Whether it's an order or request, people are more likely to respond if they can work it out for themselves. It's about decision-making, everyone has plenty of reasons to say no so you need to counter them with reasons to say yes.