T here’s a distinctive sound that an ornament makes when it falls off of the Christmas tree to its death—sort of a crunch and musical tinkling sound that happen almost simultaneously. I hate that sound. On Friday, our family decorated the Christmas tree together. This is not so much a quietly joyous occasion to which I look forward as much as an extended exercise in self-control, conducted while I perform an exacting inventory of my personal and parental priorities. Our children have been mobile for enough years now that you think I would be better prepared for this by now, that I’d have girded my psychic loins at the very least in advance of that first inevitable sound of glass breaking, but no. Every…