Bergen's research was about establishing a portfolio value that would allow for retirement without running out of cash. That is why the static spending is appropriate. Reflecting more realistic spending would allow others to retire sooner. And the 4% rule seems to ignore that at some point one will likely collect social security - so the 4% could be reduced with no change in lifestyle at all. At the end of the day, no one wakes up one day and says dang - I am on my last withdrawal.