Yes, but plumbers don't make their living from people who are too busy, they make their living from people who are ignorant. (In other words, lack of knowledge

Yes, but plumbers don't make their living from people who are too busy, they make their living from people who are ignorant. (In other words, lack of knowledge is far and away a bigger customer). I didn't say though that it was the only way, just that it was the main reason most businesses exist.