Economists describe this kind of filter (requiring higher math) in terms of separating equilibria for skills. The conceptual idea is that the separation is too

Economists describe this kind of filter (requiring higher math) in terms of separating equilibria for skills. The conceptual idea is that the separation is too costly for the low skilled group, and even a portion of the high skilled group cannot afford to pay the costly achievement. This is very much in line with Caplan's prior views. It holds true to a degree, but probably isn't universal.