Had heard of FireCalc, just went and checked it out briefly. Very interesting. Controlling spending definitely seems to be the key.
You’re right: IF you only spend $30k/yr (indexed) for the rest of your life and start with $1M at 35yo expecting to live to 85, it’s a very high probability of success.
It’s that expectation to keep spending that low that I think is naive, unless you are VERY frugal and VERY fortunate. But I agree, it does seem likely to be doable if so.
Plugged in some non-frugal numbers (used $60k/yr spending, which I could likely undercut noticeably with a little effort, but figure this provides a buffer) for retirement at 50 with a 35 year expectancy. I’d need $1.5M to get a 93% probability. Back to work....