The new HBO series I Know This Much Is True is excellent. It’s also incredibly depressing. As in relentlessly, viscerally depressing. Right now, in these times, with the lot of us passing the time staring grimly out the window yearning for a wisp of hope or uplift to come our way. It is a hell of a time—with a hell of a mood—for what ranks as one of the most emotionally draining dramas in years to make its way to TV.