When you are fearful, no other possibilities exist. You cannot perceive other possibilities or act on them properly, even if you were able to perceive them, because fear is immobilizing.
Physically, it causes us to freeze or run. Mentally, it causes us to narrow our focus to the object of our fear. This means that thoughts about other possibilities, as well as other information available on the tennis court, get blocked.
You will not think about all the rational things you have learned about playing tennis until you are no longer afraid and the event is over. You are left with thoughts like, "Why didn't I think of it then?" or, "Why couldn't I act on it then?"...
It is extremely difficult to perceive that the source of these problems is our own inappropriate attitudes, that's what makes fear so insidious.
Many of the thinking patterns that adversely affect us in competition are a function of the natural in which we were brought up to see the world. These thinking patterns are so deeply ingrained that it rarely occurs to us that the thought of our competition difficulties is INTERNAL, derived from our STATE OF MIND. Indeed, it seems much more natural to see the source of a problem as external, or the opponent, because it feels like the opponent is causing our pain, frustration and dissatisfaction.
These are abstract concepts, and most tennis players do not spend much time on them. Yet, understanding the relationship between beliefs, attitudes, and perception is as fundamental to being a great competitor as learning how to add is in math.