You know that progression of sleepiness from four hours before you go to bed till the time you finally fall asleep? I feel like the aging process can be described similarly but spread out over, say, 80 years. During the first of those four hours before you fall asleep, representing the first 20 years of life, the night is young. You’re productive, curious, soaking in information. Sleep is but a vague, distant, theoretical concept.

In the second hour, ages 20 to 40, you check your watch. “Oh, would you look at the time?” You’re still firing away, getting work done, spending quality time with your family, but time is going by faster than you expected. Now, at least, sleep is on your radar.

In the third hour, representing ages 40 to 60, you’re now generally tired, not that you’re intending to slow down or anything. But things that were easy an hour ago seem to require a fair bit more concentration. “Honey, I’m going to go lie down,” you announce.

The last hour before bed, 60 to 80: now you’re exhausted. You try to pursue a new endeavor but fail. It’s probably time for sleep soon. You say goodnight to your loved ones, you get a few things in order, and then you fall asleep.

At this point in both sides of the analogy, the jury is out as to what exactly happens next.