"Every golfer has a favourite club--a battered old spoon or a mashie with a crooked shaft--that he would not exchange for double its weight in gold. He has confidence in this club and in his ability to use it; and in actuality, he does play it better than any other. It isn't all imagination--he doesn't merely think he can play it better--he can really do so because he has confidence in it and swings it easily, freely, and rhythmically.
The better player has this same feeling of confidence, but instead of trusting one of his clubs, he trusts them all, except perhaps one. He has confidence in his swing. He is content to trust himself to take his time and hit the ball. Such an attitude is indespensible to first-class golf...
There is one kind of confidence that everyone must have in abundance; when he stands up to the ball ready to make a decisive stroke, he must know he can make it. He must not be afraid to swing, afraid to pivot, afraid to hit; there must be a good swing with plenty of confidence to let it loose.
The other kind of confidence is a different thing, and a dangerous one. In a way, it has something to do with the player's opinion of his ability to play the shots, but it works in an entirely different way. Of this kind of confidence, we must have only enough to make us feel as we step upon the tee with John Doe: 'Well, John, you're pretty good, but I think if I play hard and well, I can just about beat you.' It must be enough to overcome actual fear or to rout an inferiority complex, but it must not be sufficient to produce a careless, overconfident attitude."
So, we must have enough confidence in our ability to hit a shot that we are able to swing the club freely and without, as Bobby called it, "the gravel of uncertainty." If we don't think we can hit a shot, we are probably correct. And we must have enough confidence in our ability to beat Joe Blow, if we try hard and play well. But we must never let ourselves become overconfident.