Flat feet could be congenital (ie you are born with it) or can build with time. Most who put up with flat feet don't have any signs and usual foot function. But for others it causes pain and distress. They could be going for walks with their toes pointing outwards https://www.theorthopaedicandpainpractice.com/treating-foot-arch-pain-with-modern-orthopaedic-pain-management-techniques/