It's that way in everything, though.

I helped my neighbor fit new windows into his house without hesitation and for nothing more than a "thanks." If he had a friend that needed the same help it's probably not going to happen. Now if his friend was also there to help us out in putting in the neighbor's window, I might, as I'd then know him at least a little bit.

Or maybe if he had some of that value placeholder stuff they print on special paper he wanted to hand over. Few things motivate otherwise hesitant people like government script.