> Life isn't short--it's LONG, and you have a brief moment in that life to maximize your preparation for the rest of it.
The reality of life is that you don't know how long it will last, or for how long you'll have the physical, mental and/or emotional health to enjoy it.
You could make hay while the sun shines, only to get hit by a typhoon (literal or figurative) and find that no amount of money will restore your ability to enjoy life to its fullest. Wealth can't always buy health, and when your number is called for good, there's no amount of money you can pay the Grim Reaper to spare you.
My mom used to work with a man who was big on the "make hay while the sun shines" approach to life. He had his Hawaiian retirement planned out to the last detail and even though he was able to retire early, ran the numbers and delayed retiring by a few years so that he could further maximize his pension.
He did make it to Hawaii, but died less than a year into his retirement.
> Every morsel you make and save early means your retirement comes earlier. There will never be a more efficient time to earn those days of leisure that will come later if you stay healthy.
But what is "retirement"?
The biggest flaw I've personally witnessed with this line of thinking is that when you're young, your concept of "leisure" and what you'd do with "leisure time" is different than what "leisure" and "leisure time" is realistically going to look like as you age. Put simply, a day of leisure isn't the same at 25 versus 55. Heck, it's not even likely to be the same at 25 versus 40 for the average person.
While this doesn't mean that older people aren't able to enjoy life, even the healthiest people 50+ on average have various issues that people in their 20s and 30s typically don't have. These issues can make it more difficult and/or less pleasurable to engage in various activities, especially those that are highly physical or require peak mental acuity and stamina.
As an example, I'm an avid traveler. Elderly travel doesn't look anywhere near as pleasurable as young and middle-aged travel. And I've been to plenty of places where older people are highly limited in their ability to enjoy activities (i.e. you're far less likely to be able to trek 15km in steep, jungle terrain to catch a glimpse of a rare species when you're 65 than when you're 35).