" The question arises : How do you increase your ability to maintain concentration on the ball (or whatever your focus might be) for long periods of time. On this subject something can be learned from Bahkti yoga. Bahkti is the yoga that aims at achieving perfect concentration of mind through devotion. Indian yogis in particular have recognised the power of love in overcoming distraction of mind. Bahkti yoga teaches that love of the object of concentration makes it possible to focus one's attention without wavering, and eventually to become one with that object.
There is a story told by holy men in the East which may make this point more memorable. A seeker after Truth sought out a yoga Master and begged him to help him achieve the enlightenment of perfect union with his true self. The Master told him to go into to a room and meditate on God for a long as he could. After just two hours the seeker emerged distraught, saying that he could not concentrate, since his mind kept thinking of his much beloved bull he had left at home. The Master then told him to return to the room and meditate on his bull. This time the would-be yogi entered the room and after two days still had not emerged. Finally the Master called for him to come out. 'I cannot; my horns are too wide to fit through the door.' The seeker had reached such a state of concentration that he had lost all sense of separation from his object of concentration. "
-fron W.T Gallwey's The Inner Game Of Tennis