A difference between 2 degrees can mean 2 inches of rain 12 inches of snow. It's a nonlinear system, and the hallmark of nonlinear systems is that small chances can have big impacts.
The electoral college makes the US election a nonlinear system. A small change in vote numbers here and there, concentrated in the wrong way, can make a huge difference.
Clinton won the popular vote by about 1% point. 538 had Clinton up about 3% points. The total error of the polls was pretty small, but the errors themselves were in critical areas. In particular, Clinton did really well in states that she had no chance to win or lose, like Texas and California.
Nonlinear systems are just not very intuitive and just don't seem fair, but they are all around us, and we need to understand them to view the world in a more complete way.