I'm 100% AGAINST doing it for a "guaranteed win" :-)
First of all, there may be a direct relationship between effort and win when you're an unfit twenty-something, but if you get an injury - or just if your body gets older - you may be struggling to get back to the level you've been at before.
But, even more importantly, if you do sports with a "I have to win"-attitude, you'll start comparing yourself to others, and you'll always find someone who is better than you. Just don't start to be competitive. You're doing the sports for fun. Learn to enjoy sports for it's own sake, and you may be able to take that attitude towards other things in life.
(I've got a failed startup behind me, and one of the things that kept me sane was regularly going bouldering. Pro-Tip: Get a yearly membership as a birthday or xmas present from your parents or so. Even if you're in serious financial troubles, your membership will be paid for. Huge relief!)