10 simple things that are deceptively complex

One of the coolest Listverse lists I've yet read. 

http://listverse.com/2014/05/14/10-simple-things-that-are-deceptively-complex/

Did you know that the proof for "1+1 = 2" is 372 pages long? That rock-paper-scissors is the world's most serious game? That no one really knows how bicycles work? Click the link!