I have a relative who likes to chop wood. If you get him near a pile of firewood a few hours later you will have a stack of nicely split and stacked firewood. Nothing makes him happier. It's a gift to be sure you have a pile of wood waiting when he comes to visit.
I was at a party a few years ago. The large extended family to which I am now loosely related. The house was full of proffessionals of various strips; doctors, lawyers, artists, advertising executives. Young people, old people, children, dogs.
The meal included a large peice of meat. At one point I volunteered to make gravy. I learned to make gravy from my mother. It's really very very easy. You need to know the trick.
The person pulling the large piece of meat from the oven was excited. "Oh, cool you know how to make gravy?" The word spread. Apparently this family didn't know how to make gravy. My family does.
Later over the meal much amazement was evinced over my gravy.
Much of open source taps into this magic. The magic that one person's needs and desires are sometimes trivial for another to fufill. The talent to chop wood, to make gravy is not scarce to those that have it. Those talents are only scarce if you don't have them. Those with a particular esoteric, or not so esoteric, talent can contribute it lightly; often at close to zero cost. To the community at large, these tiny zero-cost contributions can seem like great achievements.
Of course this ain't the whole story - plenty of other stories to tell - but for this story to work you need the pile of firewood or the large piece of meat to appear in the peripheral vision of those with the talents.