Having a sick child is never easy. But if your child has to be sick, hope for something mechanical: a broken bone, a gash that needs stitches—something that can be physically mended. Failing that, wish for something commonplace. Chickenpox, a bladder infection, bronchitis. Doctors can manage these things with their eyes closed. If pushed, consider the merits of illnesses that are at least well understood—illnesses that can be definitively diagnosed and have generally agreed-upon courses of treatment. What you least want is something obscure, something not yet well characterized—and least of all, something both obscure and pertaining to the mind.