I grew up close enough to the ocean that we spent a day or two a week swimming and sunning on the beach. I was a pretty confident swimmer since I spent many hours in the pool training for swim meets. But even as a strong swimmer, I would get knocked down by a big wave every now and then. Pushed underwater, sand and water swirling around me, waiting a few seconds for the wave to pass. When I felt calmer water, I would pop my head up for a breath of fresh air.