alt Hacker NewsFWIW, the 4% rule is for safe withdrawals for around 30 years of retirement, as in, you retire at 65 and you hope to live until 95, and even then it has a non-zero chance of running out of money. It's not a percentage you should use if you want to retire at 40.
At $4 million, GP might have been hand-waving a 4% annual rate of return and keep the principle intact.