6. Monsters
This one is pretty obvious. Hitchcock's "bad guys", with extremely few exceptions, are human. Yes,
The Birds has, well, birds - but that's about it for non-human horror.
In Hitchcock's mind, murder and suspense was the height of terror. I tend to agree with Hitchcock on this one. I love a good monster movie, but humans scare the hell out of me.
7. Impossible Situations
How likely are you to run into an immortal killer at your local campground? How about a guy who haunts your dreams and relentlessly pursues you even after you awaken? How about a man who turns into a wolf once a month? Not very often. A huge chunk of potential horror is lost when the "monster" is impossible to fit into your neat little corner of the world. The monster becomes unreal and therefore just a little less scary.
On the other hand, how likely are you to run into a momma's boy who kills women in order to feel he has some power over the female sex? How about a husband who's trying to murder his wife? Or maybe a killer stuffing a body into a trunk? These aren't situations you tend to come across while drinking a latte on your way to work, but you've surely HEARD real-life examples of these scenarios on your car radio while drinking a latte on your way to work. And that, my friend, is the point of Hitchcock's thrillers - they COULD happen to you.