The raw number is for people who are not wealthy yet and have not thought through the details.
Every wealthy person knows these things and lots more.
1) If you did not earn it, you will have a hard time keeping it. Simply because you probably lack the skills to manage it, which you would have acquired if you had earned it.
2) Age matters, i.e. earning potential and future needs. A 25yo has potential, while above 65 you have little. At 35, you got to make it last 50-60 years. That is a LONG time. How many wars, market crashes etc. in just the last 20 years?
3) Cash flow matters. You have to make your yearly expenses. So just like trading, being too conservative, you slowly grind away at your wealth, being too aggressive you can lose large portions. Then you need health care*.
"People" say you need 10 mil, AFTER taxes. 5 Mil for your ex spouse. Remaining 5 mil goes something like: 2 mil for home(s) and another 1 mil in low risk to maintain them. leave you about 2 mil for discretionary investments or low risk to make your yearly expenses.
10 mil AFTER taxes is more like 18 mil before......
So get to work!
* Health care is about 13-15K a year in the open market. And you have not even gotten injured or sick. But ICU is about 25K a day. So a 10 days stint will probably cost you about 250K for the ICU and about 100K in other services.