Steve Jobs, in an interview with Playboy mag in 1985:
Playboy: Most computers use key strokes to enter instructions, but Macintosh replaces many of them with something called a mouse–a little box that is rolled around on your desk and guides a pointer on your computer screen. It’s a big change for people used to keyboards. Why the mouse?
Jobs: If I want to tell you there is a spot on your shirt, I’m not going to do it linguistically: “There’s a spot on your shirt 14 centimeters down from the collar and three centimeters to the left of your button.” If you have a spot–”There!” [He points]–I’ll point to it. Pointing is a metaphor we all know. We’ve done a lot of studies and tests on that, and it’s much faster to do all kinds of functions, such as cutting and pasting, with a mouse, so it’s not only easier to use but more efficient.
(via Cult of Mac)