Shoes; critical to your health, crucial to comfort, difficult to fit. But do I see people raving about how they've gone into a shop and now they "know their true size" and it's changed their life?
No I do not, because that would be silly. Everyone knows that shoe sizing is a bit variable, depending on the style and the brand and the materials and stuff.
Why the $%*& does no-one apply this logic to bras? Why do people think bras are somehow magically exempt from the issues literally every other garment bar slankets faces? Bras are not magic! You do not have ONE TRUE BRA SIZE TO RULE THEM ALL!
Oh yes, also, you're probably still an awesome person, not a size label.
Shoes or bras, which do you reckon there's solid peer-reviewed medical evidence for needing to get a good fit on?