Earlier quoted context omitted.
Because panicking when you're being rag-dolled by even smallish waves can kill you, let alone waves of consequence. I don't have the words to describe what it feels like to be pushed to the bottom of the ocean by a wave, then just as you feel like you're running out of air be pushed back down by the next wave, and the next wave. You have no idea which direction is up and which is down, or how long it's been since you…
Not the most convincing advertisement
For some it's sobering, for others it's terrifying.