The Sufi, therefore, learns and practices to discern the more deeply engraved lines by the observation of their offshoots. Therefore, he is able to learn more from a person's thought than anybody else, just as by looking at a leaf of a tree one can find out what kind of tree it is. As a rule, every thought a person expresses has at bottom a connection with some deep feeling. The reading of the deep-set line is like reading the cause of the person's thought. The knowledge of the cause can give greater understanding than knowing only the thought. It is just like standing on the other side of the wall. Thought is like a wall; behind it - the cause.