It's a matter of preparation really. "Willpower" is just raw material, without any form of tempering it's moot against a decent Psychomancer. So long as your brain has a pulse (And even than) and Psychomancer can break your will. How easily depends on their skill, and maybe if you've been taking your required lessons.

Basically, take Satori's classes, and you might stand a chance. But you want to rely on your own "Willpower" or the assumption that you're "natural" ability will pull you through? You're gunna have a bad time.