This is a story told by holy men in the East
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 a room and meditate on God for as long as he could.
After just two hours the seeker emerged distraught, saying that he could not concentrate, since his mind kept thinking about 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 yoga entered the room and after two days had still not emerged. Finally the master called him to come out. From within the seeker replied, "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.