Imagine that you are sitting across from a friend. There is a screen between the two of you. Now in social media, that screen has three modes. It may be a mirror, and you see yourself reflected. Or it is a surface, and you see what your friend has posted on it. Or it is a window, and you can talk through it with your friend. Design requirements are different for each mode. In the mirror mode, the interface should present an engaging and compelling reflection. In the surface mode, it should organize and structure content and navigation. And in the window mode, it should become transparent and unobtrusive.