Just that really.
I went to lessons as a kid with the school and failed, private lessons after that when I was a bit older and failed, and tried again in my late teens, but I just can't do it, it feels impossible.
I can kind of swim underwater for a short while, but can't get back up to the top, so no good unless I have a really long snorkel 
I tried really hard, and I don't think it's fear that's holding me back, because I really want to be able to do it, I just physically can't.
I'd love to have one last try at it now, but people laugh when I tell them I can't swim so I'd feel a bit embarrassed trying to learn as an adult
But it is a skill I'd really love to master, and I think an important one.
Just curious what others think? Is it possible for it to be impossible?