My favourite example is the "click start to shut down" joke. It's not a joke, it's good design.
How do they know it's good design? Did they think long and hard about where people would click to shut down? Maybe, but the more direct reason is they had user testing labs, and at the end of the test they asked users to shut down the computer, and almost all of them clicked on Start.
How do they know it's good design? Did they think long and hard about where people would click to shut down? Maybe, but the more direct reason is they had user testing labs, and at the end of the test they asked users to shut down the computer, and almost all of them clicked on Start.