Flat feet could be congenital (ie you might be born with it) or can develop after some time. Most who are afflicted with flat feet have no signs and usual foot functionality. But for Some others it causes pain and irritation. Typically used in the treatment of tennis or golfing https://www.theorthopaedicandpainpractice.com/treating-foot-arch-pain-with-modern-orthopaedic-pain-management-techniques/