Let's assume you're 40 years old and have $5M invested. Using the Guardrails Approach, you could withdraw 5% of that, so $250k a year. Even without SS benefits, that's not a bad annual budget, especially if at least some of it is from Roth or taxable accounts.

If you want to be far more conservative, which is reasonable considering that you're quite likely to survive for over 30 years, you could reduce your initial rate to 4%, and use guardrails at 4.8% and 3.2%. In this case, you'd have to live on $200k a year. Still, not a bad life unless you choose to live in a high-cost location like the Bay Area.

Using this approach, you should have millions left over when you die, so your heirs would still get a nice chunk of change (if you have the typical 2-3 kids, they'd each likely get at least $1M).

All this is assuming you bring in zero non-investment income, which at age 40 seems unlikely. More likely, you'd engage in work you love with people you enjoy working with/for. If you bring in even $50k a year from such work done at part time, the above numbers increase further.

Of course, none of this amounts to building truly generational wealth. For that, you'll need to reach UHNW level (>$30M), which is a whole 'nother thing.