The dress, blue and billowing, appeared out of nowhere and vanished right back. Maybe it never really existed? The facts don’t matter much. This is a different kind of knowing. The dress, a perfect fit, taught me the most unusual and subtle of Jewish commandments: Know yourself by transforming yourself: turn reality upside down, silly and sacred, for just one day a year. A mask of sorts, the dress transformed me into another, teaching me how to be my very self by being, briefly, not myself at all.