this repeated action causes the sections to bow and eventually crack. strong winds and collision by a vehicle or other object can cause instant damage, or just speed up the process. the good thing about sectional type garage doors is that individual sections may be replaced without having to purchase a complete new garage door.
third, are the hinges and rollers. every time the garage door opens and closes, the hinges bend and twist, which eventually will cause the hinges to crack and break. if they are not replaced immediately, this can cause more extensive damage to the garage door. with the rollers, many rollers are metal and have ball bearings. 