Also to add to that, a sense of randomness and deception is definitely great. To elaborate on that, I believe things shouldn't pop up when expected, but neither should they pop up when not expected to be expected too many times that it becomes expected. Randomness is fine, if controlled, and not given to chance. Ao Oni's random Oni Spawner was repetitive, and yes, it will always increase your Heart Rate a little, but it becomes bland and expected all the time. To have a player fight an enemy after coming
out a room would give a nice scare, but then to make the player go through four rooms after with a song that steadily builds tension but never happens is more entertaining to me. Perhaps put a cherry on top by leading the player to a safe room right after the tension build up with an abundance of light, and a gun to find with one bullet only to be confronted by a surprise party by a monster or two, and not even allow the player to have enough to fight back, but to run back into the darkness where he came from. And also, the 'deception' part adds to this. Where you expect something to happen, but it never does, but you keep your guard up, until
it slips away after a series of less hostile events and then BAM, made you flinch! And then never knowing when to bring up your guard, or put it down for the whole game.
I do like it lot more when shadows creep in the background and do not chase you, but run away, instead of something popping up with a loud sound effect to make you jump as it runs toward you.