I hear this sentiment often, and I'm inclined to believe it applies to the majority, as the majority are extroverts. It doesn't apply to me, though. I even think the performances by the two leads did the film a tonal disservice (that's not to say I dislike them), so what made the movie effectively scary for me were such things as the director's use of space and his temporal manipulation (slo-mo, slow acting, lingering shots, etc.).