I believe the figures also look to 95% confidence rather than 100%, so for instance from https://www.bogleheads.org/wiki/Safe_withdrawal_rates
![Image](https://www.bogleheads.org/w/images/d/df/TrinityTable3.jpg)
4% SWR and 30 years had a 95% success rate, whereas 75/25 stock/bonds had a 98% success rate. The choice of a 95% confidence/success-rate is perhaps based on there being less of a chance of a 65 year old retiree actually getting to live until age 95. Or if they do perhaps not having any marbles left and at which time their living costs are perhaps funded out of having sold their home to fund all-inclusive care-home costs for their remaining time.
If in the worst case you secured stock at a 20% discount to the worst case, i.e. stocks declined shortly after another started a 4% 30 year SWR withdrawal from a prior peak/higher-price, then that suggests that the later investor who bought at a 20% discount might reasonable see the support of a 4 / 0.8 = 5% SWR, or that might have also run with a 4% SWR but with a higher probability of success/residual-surplus at the end of the 30 years.
SWR is the simplest measure/method. Others employ Variable Percentage Rates that are suggested as being safer/better. Where if its running well the amount of income drawn is increased, or if things aren't running well you modestly cut back on withdrawals; And also adjusts for how much time you envisage you have left https://www.bogleheads.org/wiki/Variabl ... withdrawal