One of the requirements of acquiring control over thoughts is to become fully conscious of what they are. They have to be attended to before they are controlled. In ordinary introspection it is often not possible for the beginner to devote adequate attention to all the shadowy thoughts which pass through his mind. It is therefore helpful for the aspirant occasionally to write down all his thoughts as they come, and then to inspect them carefully at leisure. This process is different from writing planned articles. Thoughts are here left without any direction or restraint, and are allowed to appear as they come, so that even repressed elements from the subconscious mind have an access to the conscious mind.
“In a more advanced stage, an intensive awareness of mental processes can take place while thoughts appear in consciousness, and writing becomes unnecessary. The watching of mental operations should be accompanied by critical evaluation of thoughts. Thoughts cannot be controlled except through the sense of their value or lack of value. When the diverse types of thoughts which assail the mind are critically evaluated, and the internal stirrings of sanskaras are faced, understood and taken for what they are worth, the mind is freed from all obsessions and compulsions in relation to them.”
-Discourses, 7th Ed, p237