If you had a steady wind of 12 km/h toward East, how would you align your sailboat for maximal velocity?
My intuition tells me that the sail needs to be perpendicular to the wind and behind the wind, so that it can be pushed forward with maximal force. However, it turns out that a sailboat is fastest when its sail tilted at about a 30 degree angle against the wind. A sailboat steered correctly wind, can zig-zag its way upwind 2-3 times faster than the speed of the wind itself. To better understand how sailboats work, check out this video.
Despite knowing this to be true, my mind hurts when I try to figure out how sailboats work. In the past, I understood sailboat sails to be analogous to parachutes. However, the key to understanding them is to discard that analogy and replace it with another. Sails actually work more like airplane wings.
The hardest part of learning something new is not embracing new ideas, but letting go of old ones.