It's possible and achievable without major sacrifices with high probability, if you're reasonably well paid.
The basic tricks are (1) put a really substantial fraction of your income, at least about half, into savings -- index funds or similar -- and (2) learn to live a less gratuitously-spendy life than is normal in the affluent West, especially in the US. I strongly endorse both of these; but living on half your nominal income is much much much easier, and requires much much much less sacrifice, if that income is $100k/year than if it's $30k/year.
And if your investments misbehave badly enough, you're screwed. Firstly, if you hit a bad market crash before you were hoping to retire, your retirement date gets pushed out. Secondly, if the longish-term performance of the market turns out to be anomalously bad, you run out of money after being retired for years. You're supposed to save enough that the risk of the second failure mode is really low, so the question here is how comfortable you are with inferences like this: "Over the last 100 years or so, there's been no 40-year period in which you'd have run out of money if you held a broad stock-market-index-like portfolio and took out 3% of the initial capital, inflation-adjusted, every year; so you're safe adopting such a strategy now."
(I do not know whether the specific statement in quotation marks there is correct. There are studies whose conclusions have something like that form. Look them up before making retirement decisions.)
[EDITED to add: Just to be clear: I really do think the mustachian approach is a good one, and I follow it myself, and I do think anyone reasonably well paid who follows it has a very good chance of a comfortable early retirement. But I prefer not to see these things overstated, and I prefer to avoid formulations that -- wrongly but seductively -- encourage wealthy people to look down their noses at poorer people for whom living that way is very much harder.]
That is absolutely true, although "reasonably" in this case works for average American household income (about 50k) if you don't live in a very high cost of living area. The same techniques that let a middle to high income household (50k+) retire early only let a 30k household make ends meet and save some money to retire comfortably around the "official" age of 65, but that's still much better than most Americans do. His thoughts on hedonic adaptation are pretty much the same as we talk about here (having probably drawn from the same ...
Quick summary: "Hidden rationalists" are what I call authors who espouse rationalist principles, and probably think of themselves as rational people, but don't always write on "traditional" Less Wrong-ish topics and probably haven't heard of Less Wrong.
I've noticed that a lot of my rationalist friends seem to read the same ten blogs, and while it's great to have a core set of favorite authors, it's also nice to stretch out a bit and see how everyday rationalists are doing cool stuff in their own fields of expertise. I've found many people who push my rationalist buttons in fields of interest to me (journalism, fitness, etc.), and I'm sure other LWers have their own people in their own fields.
So I'm setting up this post as a place to link to/summarize the work of your favorite hidden rationalists. Be liberal with your suggestions!
Another way to phrase this: Who are the people/sources who give you the same feelings you get when you read your favorite LW posts, but who many of us probably haven't heard of?
Here's my list, to kick things off: