quite honestly this belongs in the beginner's circle, but I'll let it slide for now due to the current lack of content in this forum.

never playing worse high cards than AJ = leak. Work on your post-flop play.

playing hands like 82o = leak. There's opening your game up and then there's being a fish.

And there still IS guessing as to whether or not you have the best hand. More accurately, you can make reasonable estimations as to what kind of range your opponent has and the somewhat easier decision on how to best play against that range. Unless you only play the nuts, you can't always have the best hand.