"Someone told me that each equation I included in the book would halve the sales. I therefore resolved not to have any equations at all. In the end, however, I did put in one equation, Einstein's famous equation, E = mc squared. I hope that this will not scare off half of my potential readers."

It just feels like that law can be adapted to: for every step and pre-requisite in your setup, you lose half your potential customers.

Of course, it's not precisely that, but it feels the same.