You may have thought you learned all there was to know about your 3000 body parts in biology class but what your professor failed to mention is one of the most important parts of sneaker knowledge. Which side of your foot is the medial side and which side is the lateral side? Easy enough, the medial side is the part that your arch is on, or the inside of the foot. Unless you have two left feet. If that's the case, buying sneakers must be one hell of a task for you.