If you have flat feet, you probably already know that not every cute shoe deserves access to your closet. Some shoes feel perfectly fine for the first 20 minutes and then, somewhere between running errands and standing in line for coffee, your feet begin sending angry little messages up through your ankles, knees, and lower back. By the end of the day, you are wondering why you paid good money for footwear that seems personally offended by your arches. Flat feet, medically known as pes planus, simply means the arches of the feet are low or flatten when you stand. Plenty of people have fl...