In the trailer, you're seeing the effect essentially under a microscope, plus you exactly know what is about to happen, plus you can rewind it. These are circumstances that don't exist in the real world.
I'd urge you to give this a try. It's hard to know how powerful it is without just going out, being bold and doing it. You'll meet magicians who perform this all the time, who never get caught.
I know it can be hard to believe, but it's way less obvious when you're not primed to watch out for it.
I couldn't have put it better. Obvious to us (that's arguable, is far from obvious to a spectator. Especially those, like most, who are simply having fun by the mystery and being entertained.)