In 1974 Ernő Rubik, who taught design in Budapest, built a small cube to see whether its pieces could turn without the whole thing falling apart. They could. He gave it a few twists, and then it took him about a month to get it back. For that month nobody in the world knew less about solving it than he did, because nobody else had one. Making the puzzle gave him no head start on the way home; the maker and the stranger set out from the same corner. Knowing how a thing was put together, it turns out, is not the same as knowing how to undo what you did to it.