"In tennis, you can make a couple of mistakes and still win. Not in golf. I played three rounds in that Tahoe event, and I was drained. Mentally, not physically"

Pete Sampras is referring to the difficulty of playing golf compared to tennis. In tennis, a few mistakes can be made and still result in a win, however in golf, errors can be costly and can lead to a loss. He is also referring to the psychological pressure of playing golf, which is much higher than the physical pressure. He mentions playing three rounds in a Tahoe occasion, which likely took a lot of mental energy and focus. This quote shows that golf is a far more psychologically requiring sport than tennis, which it can be draining for even the most knowledgeable gamers.