You'd be surprised.. Psychological horror is a very interesting sub genre, because it creates fear and tension by working on the mind, whether it be yours or the characters themselves' minds. It puts together all of the tension, suspense, paranoia and all of those beautiful composites that assembled, architect a masterpiece in terms of film making. If it doesn't make you think, if it doesn't leave you questioning long after you've watched it, they're doing it wrong. Psychological horrors and psychological thrillers in my opinion are the sub genres of some of the best films around! :D