I always post this, but here goes again.
Aiming for a super low withdrawal rate is just a way to front-load your FIRE "failure" in most cases, by working much, much longer than you need to.
Remember that the Trinity study assumes you won't make any further income (almost certainly not true for people on this forum), ever, and that you have very little flexibility about spending (again, not true for all but the most extreme cases who are living on $6k a year or whatever).
Your odds of running out of money as a person who has actual useful skills and likes to do things anyway and is willing to sell their car and take the bus if needed are insanely low. Stupidly low. Even if you're FIRE at 30 and will live to 95.
With a normal 4% withdrawal rate (million bucks invested, $40k spend), at 80/20 stocks/bonds that 65 year retirement succeeds 80% of the time.
Pretty damn good!
Add just 10% spending flexibility and you're at 90% success - and that's without making a dime, ever again.
Make just a measly $2000 a year from ages 30-50 (my wife earned about that much last year substitute teaching for about 2 weeks) and you're at 98% success.
Social security is not included in that.
I could go on and on.
Your failure risks have to do with lifestyle inflation/changes (get married and have 8 special needs kids, decide your dream is yachting, not thru-hiking), death from a variety of reasons (95% of male 30 year olds won't survive to 95 anyway), and black swan political/natural disaster stuff (Yellowstone erupts, nuclear war, your ethnic group becomes persecuted, etc). Not running out of money.
-W