First the mind judges the event, then groups events, then identifies with the combined event and finally judges itself. - Timothy Gallwey

The ability to focus the mind is the ability to not let it run away with you. It does not mean not to think — but to be the one who directs your own thinking.

we tend to think too much before and during our shots; we try too hard to control our movements; and we are too concerned about the results of our actions and how they might reflect on our self-image. In short, we worry too much and don’t concentrate very well. To gain clarity on the mental problems in tennis we introduced the concept of Self 1 and Self 2. Self 1 was the name given to the conscious ego-mind which likes to tell Self 2, you and your potential, how to hit the tennis ball. The key to spontaneous, high-level tennis is in resolving the lack of harmony which usually exists between these two selves. This requires the learning of several inner skills, chiefly the art of letting go of self-judgments, letting Self 2 do the hitting, recognizing and trusting the natural learning process, and above all gaining some practical experience in the art of relaxed concentration.

Abandon” is a good word to describe what happens to a tennis player who feels he has nothing to lose. He stops caring about the outcome and plays all out. It is a letting go of the concerns of Self 1 and letting in of the natural concerns of a deeper and truer self.