Here's a scenario:
You FIRE at, say, 30. Two years later, market crashes, you decide you don't like what would be, say, a 10% withdrawal that year for living expenses, so you go get a job. Maybe it's not as lucrative as the one you had. Maybe it only pays HALF of what your old job did. But you had a savings rate > 50%, so you're still saving money even at this new, much lower paying job.
You buy some stocks while low, and over the next year the market recovers. You quit, and try FIRE #2. Having survived that crash in what would have been year 3 of your original ER, the market is pretty good for the next 8 years or so until the next crash, and by then your portfolio's been humming along for a decade, you're past the major part of the sequence of returns risk, and having not elevated your lifestyle, your portfolio has grown to a point where your SWR that was 4% is now at 3% and dropping, and you ride out the next crash easily without even thinking of going back to work.
Yes, your ER failed that one year early, but damn, to me that sounds pretty good. A two year sabbatical at age 30, then one final year of working after age 30, then ER forever? Awesome.
That, however, would be counted as an ER failure.
/shrug
Okay. I'm okay if my ER "fails." If I have to go back to work in a decade, well, at least I spent my 30s traveling, raising kids, and enjoying my life. So I go back to work for a year. Maybe even two! I don't think it's likely, but if it happens, I'm okay with that ER "failure."
I 100% agree with you, AnonOne. Going back isn't the worst thing in the world, other than for someone's pride, perhaps, if they care about that sort of thing. Yes, you may not make as much if you do go back, that is a risk you take. The risk you take by not ERing sooner though is giving up extra years of your life, and it's not just a risk, it's a definite. I'd rather risk making money at a reduced rate a but in the future as an unlikely maybe, then give up precious time for sure.