You have to create value commensurate with the return you expect. If you're exceptionally clever or knowledgeable, you may be able to create a lot of value in a relatively short amount of time, then implement a system that allows you to continue to benefit from that value indefinitely - the sort of thing described in the Four Hour Work Week.

People fail because they ignore the need to create value. They fall for sucker schemes that promise vast reservoirs of cash on tap if only you know the secret. There are rare opportunities that arise from market inefficiencies, but you can bet your ass that if someone has identified one of these opportunities, they're not going to cut you in on it.

If you want passive income, you need to create something of real value, then work out how to sell it. It's usually easier to identify the market first, then find a product to sell to it, rather than vice-versa. There are an infinite number of possible products, but relatively few viable markets.