Once, on a summer trip to Norway, I jumped in to the Arctic sea.
I did it because everyone else was doing it (yup) with what looked like ease...
And, I've been swimming since I was a tiny...one of the only things my parents were adamant me and my brothers stuck with...so I figured I'd be strong enough.
The cold was such a shock to the system I had to be pulled back out, gasping and numb.
When I swim in the ocean now, I step into the water slowly and with great care and although I rarely think about that time in Norway, it always feels as though I'm absentmindedly touching a scar.