When I was in high school my science teacher began growing a beard. Then one day he cut it off. When he came to the school that day all clean–shaven, everyone asked about his beard and why he had cut it. After we all settled down he informed us that he had been dying his hair black, and we’d never noticed.

He was a gray–haired man when he began growing the beard. Slowly he began coloring his hair in sections, while growing this very strong beard. We were so taken with the beard we didn’t notice that he was subtly and slowly changing his hair color. On the day he chopped off his beard, his hair went fully black—but not one kid in that classroom noticed. We wouldn’t have known at all if he hadn’t explained it to us after the fact. He had deliberately focused our attention on the wrong problem in order to achieve his real goal.

I never forgot that story, and it still shapes the way I think about interaction design.

Jeffrey Zeldman.