Now green’s on the other side. What happens? It takes longer to hit the button.
How much longer? Well, not much. The reaction times are usually about half a second, and the difference when the button is on the wrong side is about, oh 25 milliseconds, about 5%. It’s not much, but it’s on the order of the time Jef Raskin, in his book The Human Interface, cites as how long it takes to move your mouse cursor. It’s the right kind of length of time to be significant in whether an interface feels familiar or not.