Q: Why is a concave sole desirable?

A: Concavity of the sole is a far better sign than a ‘flat foot’. Part of the foot’s shock-absorbing mechanism is the ability of the sole to drop when weight is put on the foot, allowing the hoof wall to flex, and in some situations to improve traction (grip) by ‘cupping’ on softer ground. If the food is flat it is unable to do this, so the shock-absorbing function of the sole is much lower. This does not bode well for the joints above.