Certain things in life just seem like a guarantee; your paychecks will get taxed big time, you only have a certain amount of time to live, and above all else, as you get older it gets harder and harder to stay awake through an entire day.
It's amazing how drastically this happens too. When you're in your teens and early 20s, you can easily stay up til 5 AM finishing your homework (because last-minute is best minute), get an hour of sleep, head to class, and somehow manage to be perfectly functional the entire day! Hell, you can even do this a few days in a row and not start to crash til much later.
Soon as you near your 30s though, things start to slow down. Suddenly you're taking longer and longer naps as soon as you get home from work, and once you hit retirement, you're starting to nap even more regularly than you're actually awake!
Nobody is exempt from this; whether you work in construction, data input, sculpting, or even freaking writing for an internet news site, everyone ends up needing more and more sleep to function. As it turns out, even the Pope is susceptible to this, as Pope Francis has admitted that he can't always keep his eyes open during prayer...