The ocean is a beautiful place full of wondrous nature, soothing silence, but also a lot of danger.
There are plenty of different types of animals that live deep down under, there are decaying bodies and remnants of shipwrecks, and perhaps more pressing - there is always the possibility your equipment will malfunction and you'll drown.
I wear contacts so getting water in my mask is extra bad as I can't open my eyes underwater. Shortly after being told about a shark colliding with my friend from behind and removing his mask I am pretty scared about this (not sharks in general.) And I see a shark heading for me. They are curious, they often shoulder bump you as they turn at the last second.
But she wasn't changing course. I stayed calm and still as long as I could and at the last second before she hit my mask I ducked. Except instead of ducking under I just headbutted her right in the nose. Everyone saw and thinks it was the funniest thing ever. I may be the only person alive who headbutted an 11-foot shark in the nose but it was because I was scared she would take my goggles off.