This is Gareth. He's playing through the early stages of Fallout: New Vegas on the PC. Why are we watching him? Because he can play it without using his hands.
Gareth, who through disability does not have the use of his hands, is able to customise a game's controls to the degree that he can play through using only the mouse. And his head. It's amazing stuff.
The human chin is not built for that kind of precision work, juggling the left and right mouse button like that. You try it, see how far you get.
Then bear this in mind next time you're complaining about a game's control setup or how you don't like a particular control pad's analogue trigger responsiveness.