There is a bone on the inside edge of the foot that goes around the arch of the foot. I forget what it's called, but Nick knows. Anyway, if you have a good arch to your foot, this bone arches up and away from the inside of your foot. In contrast, if you have a flat arch, this bone is not lifted up and towards the outside of your foot, so it sticks out to the inside. If you have a flat arch and try to wear boots with a good arch, not only will the arch feel like you're standing on a golfball, this bone will also rub painfully on the inner side of the boot. You could try and heat-mold the boots to redo the arch structure and the inner edge geometry, but it's easier to just go with a boot manufacturer that makes boots for your kind of feet. The tricky part is figuring out which manufacturers match up with your type of feet...