After giving this a lot of thought and pondering... what strikes me is that any kind of investment comes with the downside risk of losing the entire investment.
I can't see any real exception to this rule. If you own stocks, the stock market might tank at the wrong time (for you). If you own bonds or cash, inflation might hit at the wrong time (for you). If you own land or a house, some natural disaster might happen or you might fall behind in your mortgage payments or tax payments, or get hit with massive renovation/repair costs.
Given that there's no such thing as a risk-free, downside-free investment, it seems like investing needs to be thought of as an opportunity rather than as a guarantee. I can't rely on investments, but I might as well invest because the up-side is so high.
What I'm now starting to consider is semi-retiring rather than fully retiring.
I'll find some work that's not too mentally taxing, keeps me up & about, active and social and pays well enough that I can save half my income or more. I'll get used to living very frugally and basically just work 6 months on, 6 months off.
Though cash isn't a good investment, I think holding enough cash for 6 months living expenses is a reasonable risk to take. It seems unlikely that there would be sharp inflation over a 6 month period. If there is, I guess I'll just keep working for the full year.
The investments will, meanwhile, go up or down depending on the state of the economy. But they'll always be there as a fall-back, in case I need to take longer than 6 months off or pay for medical expenses or deal with any other kind of emergency.
I guess this is kind of already what FIRE advocates. No one seems to be saying that you should do nothing after retiring. Rather, you should still do some kind of work - paid work if possible. Keep some kind of non-investment income rolling in. But keep your investments in growth assets and keep your living costs down, so that you can gain maximum benefit from your investments.
You're more free from money if your job choices are dictated by health, fun and purpose. Freedom from money doesn't mean being able to survive without working. It just means that you have an opportunity to do work that's fun and low-stress, because you don't have to support a massive income in order to support extravagant and unnecessary spending.