Living really cheaply in SF is really just a question of cheap rent and never eating out. If your willing to have roommates you can get below 1k/month rent making 25k/year living expenses doable.
Granted, Heath issues, dependents, or debt can make this a non starter. But, just because most people you work with spend most of what they make every month means you need to do the same.
25k / year living expenses still works out to about 40k per year. And you have a lot of room mates. But now if it's only a quarter of your income, you need...
100k / (1 - (0.28[1] + 0.093[2])) = 159,489.
Plus if you retire, you're going to be managing your own health insurance, so the required living expenses number increases, probably by thousands of dollars a year. And it's not like you can flip from a frugal living style to a more flagrant one afterward, so you're going to have to live with room mates for the rest of your life, and never eat out, still.
There is little reason to stay in a high cost of living area while retired and even 600$/month can get you a nice place in much of the US let alone the rest of the world with the difference covering health insurance. As to income some people really do make more than 200k/year. And it’s such high income earners where such savings rates really become not just viable, but a reasonable choice.
More importantly the goal is not necessarily full retirement. Plenty of things are entertaining and make some money. Perhaps you only make 5k/year as a writer or painter well on its own that might not mean much but it can easily boost your nest egg over the next 20 years. Or perhaps teach a class at the local collage or even some of those short training classes. Not to mention long shot’s like trying your hand at acting.
PS: Your expenses often rise as you age but even just working 10 years entitles you to some Social Security benefits.
Granted, Heath issues, dependents, or debt can make this a non starter. But, just because most people you work with spend most of what they make every month means you need to do the same.