“Subjectively, a gnat doubtless feels that its span of a few days is a reasonably long lifetime. A tortoise, with its span of several hundred years, would feel subjectively the same as the gnat. Not so long ago the life expectancy of the average man was about forty-five years. Today it is from sixty-five to seventy years, but subjectively the years are faster, and death, when it comes, is always all too soon.”