> Car owners systematically underestimate the total cost of ownership by ~50% (i.e. the true cost is ~2x the perceived cost).

Fortunately, that's not me. I've been keeping all financial records for all non-cash transactions for over 15 years, and so I know exactly what I've spent on my car - fuel, repairs, addons, everything. I've posted breakdowns far down in my comment history (perhaps in the last year - not sure).

What I can say: It's not even close to whatever Edmund's TCO calculator reports - so I'm a bit wary of these estimates. I'm not frugal, and I'm not a car guy, and I do whatever the mechanic suggests.

How do you overcome the uncertainty? I paid MSRP for my current car, $23500 in July 2020. Since then it has depreciated at -$300/month. That is to say, net of energy, insurance, and annual taxes my real cost of ownership has been -$150/month. I am being paid to own this car. But no amount of analysis could have told me that at the time, and a difference of $500 either way on the purchase would have been utterly irrelevant to my happiness and well being.

A recurring theme keeps coming up in your comments:

The notion that the amount you can save is only $500. As several commenters have pointed out, it could be a lot more (pre-pandemic).

> But no amount of analysis could have told me that at the time

That you are "making" money on this car is irrelevant to the analysis. Just as totaling the car within a few months of buying it is irrelevant to the analysis. You'd still have anywhere from $500 to $3000 more in your pocket regardless of the amount (or direction) of the appreciation. You'd still get the negative depreciation you're getting now.

Again: I really recommend reading an engineering economics textbook.

> a difference of $500 either way on the purchase would have been utterly irrelevant to my happiness and well being.

Well clearly, if $500 is irrelevant to your happiness, then it is irrelevant to your happiness. No one is trying to convince you otherwise. What people are pointing out is that the $500 (likely a low estimate) you are down has the same financial impact on you as buying a Pepsi and getting charged an additional $500 for the single Pepsi. That the latter case may make you upset (or not) is up to you. We're not trying to make you feel better - we're pointing out the financial outcome is the same.

Of course, if you're simply trying to say that it's not worth $500-3000 spending the effort to get a better deal - that's totally fine. But that should be phrased as "$500 wasn't worth the hassle" as opposed to "It shouldn't matter because it is a small percentage of total ownership cost".