Unschooling: The Advantage of the Real World
We want our children to learn what the real world is like. One way of doing that is to construct a synthetic world designed to imitate the real one. To teach them that they will sometimes have work to accomplish things, even if they don't want to, we assign them homework they aren't interested in doing and reward them with grades. If grades don't work well enough, we reward the grades with cash, as some parents do.
What this approach leaves out is the causal connection between the work and the accomplishment. Someone else has told you to do unpleasant work, someone else will reward you for doing it, but there is, from your standpoint, no logical connection between the two. Doing homework does not, so far as you can tell, actually produce money.
The alternative to a synthetic world is a real world–the one we and our children are living in. If you don't tune your harp, it won't sound very nice when you play it. If you don't tidy up your room, at least occasionally, you won't be able to find things you want. If you don't sometimes do things your younger brother wants you to do, he won't do things you want him to do. That world also teaches the lesson–getting what you want sometimes requires doing things you would rather not do. And it gets the causal connection right.