I hope this will still be helpful despite my intentionally vague answers in an effort to remain anonymous.
At the risk of enraging the "retirement police," I do have to preface all of this with the following... If I were single, I'd be living my current lifestyle entirely on my investments without a problem. I've tracked my expenses for years and know for sure that I could do that with plenty of wiggle room. However, I happen to be married to a working spouse, so we're both living on his (much smaller) income while my investments grow to the point where we can both retire on them.
Net worth ~$1.75M
Region: very rural Pacific Northwest (But I did not earn the majority of my income here. For the second half of my career, I did locums, mostly in the southwest, and I had a part-time job in this area for the last year or so in addition to locums. We live here solely because we love it here.)
Investments: Vanguard Roth IRA, SEP IRA, and taxable brokerage account. Set it and forget it. I fired my financial advisor years ago. I paid off my student loans (over $300,000) 4.5 years after finishing residency, and I continued to funnel as much as possible into "buying my freedom."
Philosophically, I'm pretty much the same as WCI and PoF. The main difference I see is that they seem to spend more, or at least WCI does. I'm frugal, but not cheap, and for me, freedom for the rest of my life is worth skipping some luxuries. I pretty much buy what I want; I just don't have expensive taste, and I'm happy to DIY a lot of things. (It helps, of course, that my husband is the same way.) Some examples:
WCI's infamous $11,000 dining room table --> I bought big slabs of gorgeous local curly maple for $1500 and made a table myself
Suburban "doctor house" --> $450,000 rural house with good bones but in need of some cosmetic work on a piece of land that needed clearing but has incredible views (People who haven't been here before do a double take and then out comes the phone for photos. "Um, sir? The water pump that we called you about is over here... Sir? Excuse me?")
Heli-skiing --> trekking across Costa Rica, AirBnBs near Scotch distilleries on Islay, learning Spanish on the beach in Ecuador, etc.
Nothing against any of those more expensive options, but I knew that for me, it was more important to just get out.
You might have noticed I didn't mention kids. So yeah, we were DINK. But I don't think kids have to mean that you can't retire early. I have a friend with SIX kids in southern CA in a lower-paying specialty who is on track to retire early, too. Not quite as early, but still long before "normal" retirement age.
Side jobs: If something fun happens to pay money, great! But I'm not looking for anything just to make money.
SS: I did not count this in my "what do I need to retire" calculations. If I get anything, it'll just be a happy bonus.