What baffles me is when people are accepting of an inflation-adjusted 4% WR but think holding onto a 4% fixed mortgage is somehow 'too risky'.
I've told this story before (maybe in this thread, I can't remember) but it is well worth repeating when the subject of risk comes up. A dear friend is an MD. I wouldn't say she's mustaschian, but she's frugal and hates debt. When she got done with med school, she stayed in her student apartment and crushed her student loans. She bought nice cars, but not fancy cars and mostly saved and invested. I will say that I've observed that most doctors are pretty bad with money, because they seem to think they will always have a gusher of money in the future, so they don't think much about investing and saving, except in investing in things that they think will be home runs. A broad brush, but I think fairly accurate, so she definitely was an outlier among her peers as far as savings and investing. She told me most of her peers still are paying on their student loans, for example.
She meets a great guy who is a civil servant who makes OK money, but will never be a huge earner. They fall in love, get married, have a kid, and buy their dream house together. And by dream house, I mean dream house. It is the coolest house that anyone I've personally known has owned. It isn't particularly big or fancy, but every element of the house just works. If you walked into it, you'd think this house is totally cool. Great school district, close to work and the grandparents. It is absolutely a forever house. It was very expensive, but they bought at the bottom of the market and put down a lot of money (mostly hers).
Her plan is they aggressively kill the mortgage (just like she did with her student loans) before the kid gets to college. Then they'll have income to put the kid through college. And then cut back hours and continue to save and retire on schedule but very comfortably in their dream house.
As it turns out, they are not in love anymore, can't work it out, and don't want to be married. However, the house has appreciated a lot and they live in a community property state, so separating means she would have to cut him an enormous check for his share in the equity in the house. So that means selling the dream house, and in turn that would mean moving farther away from work and the grandparents. So what they decided to do is both stay in the house as divorced parents. Neither of them want to do this, but they can't figure out how to make it work financially otherwise so they put up with a far less an ideal living arrangement. She feels like there is a financial Sword of Damocles hanging over her head. Her retirement plan, while not strictly mustashician, is still better than 95% of the populace, is dead.
If she hadn't been aggressively paying down the mortgage she could simply cut the ex-husband a check and be done. It would be a setback, but everyone would be better off. But because the money is tied up in the house, everyone is worse off. Most likely, neither one of them will wind up living in their forever house, and both will have to move farther from work, the good school district, and the grandparents.
Everyone who advocates paying down the mortgage says something along the lines of "It makes me feel better." And that's worth something, no question. But no one gets married thinking they might get divorced. No one thinks they will be the one who is laid off. No thinks they or a loved one will have an extended illness and can't work and will need expensive medical care. If the money is tied up in the house, it can be really hard, or maybe impossible to deal with those issues. Those are real risks, and they happen to real people. People who advocate paying down the mortgage without including those risks are making a mistake. A bird in the hand is worth two in the bush. And paying down the mortgage is more like one in the bush.