My parents took my sisters and I to a Robbins fire walking event when I was in my teens.

Callouses have nothing to do with it. As long as you keep moving, the sweat on your feet provides enough protection. My sister hesitated and got a small burn.

Robbins is a complete shyster regardless (part of his talk was trying to convince everyone that the germ theory of disease was false, and that he could cure AIDS through dietary changes), but fire walking isn't a mystery.