If it helps, here is a graph of the data behind
Bill Bengen's original study that established the 4% rule.Note that he calls this magic number "SAFEMAX." Meaning, the maximum withdrawal rate you can be safe with, over an expected 30 year retirement.
Here, success is not going below $0 in a worst-case scenario. But look at how high the number goes for other scenarios. The problem is, you never know what scenario you fall into until after the fact--there is no retcon-ing of your spending, saving, and investing habits. So, planning for the worst case will likely leave you with a lot of money, but you won't go broke.
What is also interesting to me is that the Great Depression is *not* the worst case scenario. It is, in fact, the mid- to late- 1960's, which do not live in investing infamy. They do, however precede the 1970's, which featured stagflation. That is what eats into nest eggs.
Lest you fear we are in "Stagflation II," you often hear our current inflation as being at a "40-year high." Note, 40 years ago is the early 80's, after the fever of 1970's inflation, which needed mortgage rates of 18% to control, was already well on its way to recovery.