Just because he makes it look easy, doesn’t mean it is.
There is nothing in front of him. Nothing. he doesn’t even use tennis balls as a guide and all the effects are done in post. Everything we see on the screen, Robert sees in his head. He is literally acting with nothing. Just his imagination. And he does it again and again. Not just the simple holo work like the HUD but the complex scenes in the workshop where he has to remember the placement of each screen. The screens that aren’t even there. It can’t look clunky or forced, then the f/x team will have nothing to seam with. Each movement has to flow liquidly and be natural. Plus, in most of these scenes he has dialogue with JARVIS…an actor who also isn’t there. And he does it over and over again. Movie after movie.
So basically Robert is acting with props that don’t exist and in the case of when JARVIS shuts down, doing an emotional scene with no feedback but from a guy who is reading lines off camera.
Greatest actor of his generation.