I was told this can be `proved` by, if you say to a complete stranger on a train or bus who is doing a crossword or writing a letter, "GIVE ME YOUR PEN FOR HALF A MINUTE, PLEASE" they are more likely to lend you their pen than if you say, for example, "Sorry to trouble you but please would it be possible to borrow your pen, sir?"
However I am just too reticent to even try out this exercise, let alone try to put it into practice in my daily life! ANy volunteers please?!