Or nobody sells your book at all. You give it away for free on the Internet, and you make money off speaking appearances.
It's foolish besides--speaking engagements, etc. take away time from actually producing creative works. It's the sort of miss-the-point silliness often espoused by the anti-IP sorts: "spend an incredible amount of time doing X to maybe, if you're lucky, sell a marginal number of Y, where Y is totally unrelated to X."
It's silly and a misallocation of a wtiter's resources to take away from actually writing to hit the speaking circuit.
It is not, in the general case, very viable. Which is why nobody takes it very seriously as a good path for all, or even most, writers. Because they have to eat, too.
That's pretty much what most artists go through now, isn't it? I'm not convinced that copyright does a particularly good job of solving that problem. I'm not saying I definitely think copyright should be abolished, but it does at best a very mediocre job of rewarding artists.
It's not going to keep you in gold-plated Maseratis, but it can start to add up.
Do you have a free-job that consumes most of your time, and a paid-job you fit in around it?