When you get an open water diver certification, you have to read and discuss all the things that can go wrong. Decompression sickness. Nitrogen narcosis. Oxygen toxicity. Pulmonary embolism. Barotrauma. Panic. 

While knowing about these risks (and how to prevent, mitigate, and treat them) is vitally important, all that information can make your first few dives a bit nerve-wracking. Humans really aren’t supposed to be able to breathe (or function at all) at the bottom of the ocean. So scuba diving is not the most natural thing in the world—it takes some getting used to.