Therefore, the work of the mystic is to be able to read the language of the mind. As the clerk in the telegraph office reads letters from the ticks, so the Sufi gets behind every word spoken to him and discovers what has prompted the word to come out. He therefore reads the lines which are behind man's thought, speech and action. He also understands that every kind of longing and craving in life, good or bad, has its source in deep impression. By knowing this root of the disease he is easily able to find out its cure. No impression is such that it cannot be erased.