Flat feet is usually the wrong term used to describe a condition called Pes Planus. Most people that have ‘flat feet’ have not got flat feet.
There is no destruction on the arch in the foot at all.
What they do have are feet that ‘roll’ at the ankle too much or too easily leading to the arch having to accomodate the roll by moving downwards. This gives the impression of ‘flat feet’ but it is really just a compensation position on the arch.
Pes planus is a term used in medical fields to describe this ‘flat foot’ position. It comes mostly from the bodies inability to control the excessive movement of the ankle joint. This movement ‘roll’ can be aggressive and when it happens over a long period the other structures in the feey, ankles, legs and back can pay the price and produce a wide range of conditions.