That comment, by the way, was brilliant. I had thought of a similar thing, but you put much better than I could have.
Woo hoo, props from Mrs. MM
and arebelspy, two of the most valuable members of the MMM community. I'm honored! :-) Feel free to steal my comments any time!
I absolutely agree with you that someone who has been Mustachian for years and already has expenses to the level they want them, and can accurately project post-ER expenses (i.e. no work-related expenses, lower taxes, etc.) means you'll have that issue I brought up at the bottom of the OP: you will have the trade-off of working a bit more to build that cushion for asset runaway. That's likely A-OK.
Yep, it ends up just being a caveat that should be added to MMM's general "leap now, because things will generally turn out *better* than you expect" advice. But those of us who already have things mapped out that accurately are also probably aware enough to include that caveat on our own.
When I conceived the idea of early-retirement 7 or 8 years ago, I estimated that I could live happily in retirement on $20k/year. So I created a report in Quicken called "Regular Expenses" that reports my yearly expenses that I would expect in retirement, and I use that to "prove" to myself that it can be done (so far I haven't proven my estimate wrong, yay!) In reality, income taxes and mortgage interest are the only actual expenses that I exclude from that report, and reading MMM unfortunately hasn't resulted in me excluding anything more. Being single and living alone means that I don't think my going-out/looking-good expenses would decrease as they would if I was married, moving somewhere cheaper (away from friends/family) is less attractive when single, etc. So becoming an MMM-reader hasn't really affected my planning there, for better or worse.
But the part that has been truly eye-opening and enticing to me that I had not considered before MMM is "that opportunities seem to come knocking almost constantly" in retirement. I have a high enough opinion about myself to believe this might be *possible* for me, but I'm also self-aware enough to know that I'm not nearly as inherently awesome as Mr. and Mrs. MM, and I get the feeling that Opportunity spends a disproportionate amount of time wearing out the MMs' door-knocker vs. the average person's. So my challenge at the moment is trying to guess an Awesomeness Derating Factor that I could apply to myself to predict the amount of income-opportunity I could achieve in retirement. The easy option is to ignore this news that I've learned from MMM and then be pleasantly-surprised if/when it happens. But I've found that even though I have not included it in a hard-numbers way yet, it's already pervading my soft assumptions.
My plan hatched 7-8 years ago was to retire at 41 (6 years from now), and throughout my 7-8 year experiment, that prediction/hope stayed remarkably stable. If anything, I thought maybe I'd work another year to achieve an extra cushion to increase the chances of achieving "asset runaway". But now after reading MMM, his optimism for all things has me thinking 6 years would be MORE than enough, and that 0 more years might even be plenty. But which one? Or somewhere in between? It doesn't help that this new factor (income in retirement) is even less-predictable than stock-market returns or inflation or lifespan. Argh! Fuck uncertainty! :-) For now I'm still trying to keep the "work 6 more years" idea in my head, at least until I have more concrete reasons to adjust.