"For one thing, when you're playing as well as I was at the time, you think you can play with anything. That isn't true, of course, but I didn't know it then"

Payne Stewart's quote is a reflection on his experience as an expert golfer. He is expressing the concept that when you are playing at a high level, you can become overconfident in your capabilities. This can result in a false sense of security, as Stewart acknowledges that this isn't true. He is admitting that at the time, he thought he might play with anything, but he now knows that this isn't the case. This quote is a suggestion to stay modest and to not get too captured up in your own success. It is important to remember that even when you are playing well, there are still areas of enhancement and that you should never ever become contented.