Re-deriving from scratch it is hard. No question about that. Magnetism doesn't make a ton of sense either, but it's simple to demonstrate. Intuitive and simple

Re-deriving from scratch it is hard. No question about that. Magnetism doesn't make a ton of sense either, but it's simple to demonstrate. Intuitive and simple are not always the same thing. If your coin happens to be absolutely fair, it will require on average 3 flips to generate a fair flip via this method. The point is you don't know a priori whether a given coin is fair.