Maureen O'Connor - NYMag writer and former bra-saleswoman - tells it like it is, in response to "that irritating statistic that appears at least once in every issue of every womens' magazine: '85 percent of women are wearing the wrong bra size'":
[T]here is only one universal truth when it comes to fit, and it equally applies to bras, shoes, pants, socks, and wedding bands: If you put it on and like how it looks and feels, then it fits just fine. Your bra is not wrong. Your bra cannot be wrong. Your bra is underwear, a value-neutral object to be worn, replaced, stuffed, discarded, celebrated, hidden, or exposed however you want.As the kids say, or said five minutes ago: this.
But I'd take it further. The bra-fitting gimmick is to tell you that you take a cup size larger and band size smaller than you'd thought. Given that we'd all look more conventionally attractive with larger breasts and smaller waists, we try on this miracle product and lo and behold, an hourglass physique. Or, more likely, we're just flattered by the notion that we're simultaneously thinner and bustier than we'd thought. It's a more 3D version of vanity sizing. Then we get home and realize that even if it's possible to squeeze into a $60-plus contraption in the right-but-wrong size, having circulation is even nicer. Or so I've heard.
And the idea underlying this is, if you think about it, incredibly sexist. The idea that women are just too dumb to figure out for themselves whether their clothing fits properly, or that they're too lacking in confidence not to just go along with it when someone in a position of authority tells them that an item that they know fits actually does not. Because it really is possible to go into a dressing room with a range of sizes and styles, and see for yourself what fits. It's not like with running shoes, where someone will examine your stride and, in theory, impart information you couldn't have easily gotten yourself. The bra-seller may tell you - or so they say - that you should discard the bra you wore to the store, not because it's worn out, but because it hasn't been approved by (sold to you by) this establishment. Don't do this.
On a related note, that Prudie letter from the college senior who, though not flat-chested, doesn't like wearing a bra. Yes, yes, the usual Prudie titillation, but I found it telling that this woman (assuming this is a real person's complaint) mentions having been fitted for a bra. That could well be where her problems began. I'm also having trouble picturing the line of office-work for which a bra-like camisole under other clothing (blazer, button-down) wouldn't suffice, which makes me think this letter really just was about how a braless coed was braless.
My entirely sensible female commenters are chiming in to say that on the contrary, bra-fit is a real thing. Which is making me think that my problem might have been having too much confidence in a particular saleswoman at the Town Shop who estimated and didn't measure, and who may well have just wanted to sell that particular bra. (I may have had a choice of two.) There's no obvious distinction between reputable bra fitters and bra-sellers posing as such to dupe the suggestible. At the time, I took the limited selection to mean this woman had so much experience making such assessments that she just looked at me and knew.
Or it might be that these things are subjective - even among women with the build for which this is even an issue. (Without getting too technical, I can assure that I don't have a gamine physique). My sense is that it's possible to own some spectacularly fitting bras that make clothing look amazing, as well as some now-I'm-decent-to-go-out ones that don't. What fits best might be the most comfortable, but... it depends. I like the idea that these two traits could be found in the same garment, but... who knows. Comfort is subjective.