Surely someone has commentated that “life is short” in one form or another before waitbutwhy, right?

IMO it’s good for these sentiments to be rephrased and restated repeatedly. The reason is that these things have to hit you at the right time and in the right way to make the impact that they’re “supposed to.” The first 999 times someone says life is short, you shrug it off and walk straight into another day in zombie-mode (nothing wrong with that!). But the 1000th time someone says it, and you happen to have just gotten off the phone with your mother telling you she has some illness… that’s the time you need to hear it. So you pack up and move across the country.

That's the idea behind "The tail end" https://waitbutwhy.com/2015/12/the-tail-end.html