"If you took me down to the dining room," Mom asked me, "do you think I could help fold the napkins?" At this point, my ninety-year-old mother was deaf, blind in one eye, and unable to get around on her own. This once energetic, lively woman wanted more than anything to be useful. Now the only active thing was her mind. My perennial glass-half-full mother was depressed; she worried about being a burden and dreaded the thought that she could possibly...