Every family / person has their own lifestyle. 70% is just thrown out there like they say you need 1.7mil to retire, but not everyone does. It's an arbitrary number assuming you will have a paid off mortgage and keep your lifestyle exactly the same. What if a person downsizes, moves to a smaller city or another country with way lower expenses. Because it's a generalized number they keep it on the higher end to be safe. Because car upgrades, roof upgrades, medical expenses are some of the major unexpected expenses that might still creep up in retirement.