On our second day at Ann Arbor, Tracy (the other Tracy^^, our guide) and Brittany showed us around UM campus. One of the landmarks was the Diag. It's the center of diagonal roads leading to different buildings on the center campus, hence the name "Diag". At the center is a huge "M", for Michigan, and it's the custom not to step on the M.
The Diag was actually first created by students taking shortcuts to classes, and it really reminded me of a famous saying in Chinese by Lu Xun: Originally there are no roads in the world, but once many people start taking certain paths they will become roads.