There's more debate as to what would be a safe withdrawal rate over the long term without depleting principal, but I expect 3% would be a bit on the high side, although not unreasonable if one has a backup like part-time work.
Of course, that's assuming you withdraw 3% of the initial amount each year and adjust for inflation. Obviously if you only withdraw 3% of the current amount each year you'll never run out, by definition, but you might end up with shrinking spending money.
Still, just a nitpick. I agree with you in principle for sure.
In addition, we're talking about a real withdrawal rate; a 4% real rate of withdrawal will be approximately a 6% nominal rate assuming inflation sticks around 2%. It's very unlikely you're going to maintain that from a balanced portfolio over the long term without depleting principle at all. Might be possible with an all-stock portfolio if you get lucky, but significant chance of failure if you get a poor sequence of returns.
Past results do not guarantee future performance. People in the FIRE community generally look at market performance since the final decades of the XIX century. For many, even these numbers do not guarantee anything, as the growth during these days reflected USA entering its golden age. Who knows if it will last through XXI century.
at this point a reasonable response is "there are no guarantees". If the 4% rule was back-tested through the great depression and generally came out fine, it's probably in the right ballpark.
As another FIRE blogger puts it, "3% or less is a near sure bet as anything in this life can be"
https://jlcollinsnh.com/2012/12/07/stocks-part-xiii-withdraw...
If you are invested in low cost index funds, most assume you can safely withdraw 4% a year and not deplete your principal. If you're retiring at 35, you might want a greater safety margin, so let's say 3%. That gives you 60K a year.
How do you retire on 60K a year? Obviously take what I'm saying with a grain of salt as I'm a relatively young person and haven't done any of this yet. But...60K is the median household income in the US, so half of families in the US live on less. If you're retired, you can probably save in ways others can't. For instance:
* Housing. You don't need to stay in a high cost of living city, so move to a much cheaper area (maybe a college town).
* Education. You have much more time, so send your kids to all public education, and use your extra time to educate them further.
* Debt. You have a ton of assets. Why hold any debt?
* Automobiles. Bike instead, if you're physically able.
* Health. Probably the hardest one since insurance in the US is tied to employment. I understand the recommended approach here is to pay out of pocket for a plan, but many have trouble with this. Of course, the standard advice is to use the extra time you have due to retirement to stay as healthy as possible, but I acknowledge this isn't a perfect plan.
[1] https://www.mrmoneymustache.com/ [2] https://www.madfientist.com/