The old 4% swr rule can never be a one size fits all parameter with a problem so complex and fully dependent on a legion of assumptions about the long term future.
And even in the limited modeling and analysis based on the past, it only really applies to the portion of your stash in a mixed stock/bond portfolio. Not to other investments, like real estate, property development, forestry, businesses, etc.
So for me it means having sufficient passive income to meet all long term expenses for a middle class lifestyle (frugal) without having to work. So that you could literally go fishing all day.
In reality, I agree with mmm, that opportunities will come along you want to do for the sake of it, yet they will also generate income. Not relying on this income is a cushion. Do you want to count on social security? Some do, some don't. If you don't, that's another cushion. Do you count a fully owned home as part of the stash? I would say yes, but some say no, and that's another big cushion.
But I would note that most people are too conservative in their perception of risk, and thus delay FIRE because of worries about the far far future. Optimism gun fail.