woukld you swim clockwise or counter-clockwise around the world? would you have a pre-arranged route or would you just splash off in whatever direction suited you? how would you know you weren't going round in circles? where would you keep your towels, or would just swim around hot places where the sun would dry you off?
you latter-day Burt Lancaster, you!
if I couldn't fail, absolutely guaranteed to succeed, I'd go back in time and prevent humanity from evolving, because the Earth would be better off without us. But of course I'd then be in temporal paradox territory, as I wouldn't exist to go back in time in the first place, so in fact I couldn't succeed even if I was guaranteed success which of course is another paradox.