Hollywood movies work under different rules than the rest of the world. We know the terms “cartoon physics” and “Hollywood physics” to refer to actions that would never happen so conveniently or photogenically in the real world. There are certain everyday objects that the movies go to again and again, but they don’t work the same for us as they do for movie characters. Take a pillow. In the movies, killers use pillows to silence gunshots. Don’t try this in real life. It may work just a little, but never so much that you can disguise the fact that you’re shooting a gun.
That's why real (movie) pros skip the gun part entirely and use the pillows themselves as weapons -- by putting them over their victims' faces and suffocating them with comfort. It works remarkably fast: about 60 seconds in One Flew Over The Cuckoo's Nest, 25 seconds in Revenge, and a zippy 10 seconds in Vampire Diaries.
Now, it's true that, when held tightly over a person's face, pillows really can restrict air flow. And you could maybe restrict all of their air as long as you have a victim who can't, you know, turn their head (remember, you're trying to get a perfect seal over both their mouth and nose) -- so at least Jack Nicholson had the excuse of being lobotomized in his scene.
Then, there is the length of time it takes for the victim to expire. While unconsciousness can set in sooner, "often the fatal period is three to five minutes" because of course it is. Try holding your breath for a half-minute. Are you still alive? There you go.
Movies don’t have three to five minutes to wait for someone to die! So we suspend our disbelief once again. But a pillow is only one of the 5 Everyday Products That Hollywood Thinks Have Magical Power that you can read about at Cracked. As always, expect NSFW text.