Halloween is one night when strangers still open doors for each other. My wife and I still take our girls trick-or-treating. We know these years are numbered: soon they’ll be too old, too cool, or too busy. So tonight, we might linger a little longer at each door. There’s something deeply human about the whole exchange: knock, wait, smile, offer, thank. A tiny ritual of trust repeated a hundred times in one night. That’s what great products do, too. They build small, repeatable moments of...