Here's the deal: you want to drop a coin into a container of water. Maybe you're bored. Maybe you're trying to win a bet about hitting a submerged target. What's the best way to drop the coin so that you can hit that target? The easiest way is to drop the coin perfectly flat, with its faces parallel to the water's surface. Provided there aren't any currents or turbulence in the water column below, the coin should drop straight down.