It is necessary to reject thoughts that continually infringe upon your mind from your present environment and to carefully select each thought that you generate in order to reach a state of true mental maturity.
You might ask how it is possible to select thoughts of value from thoughts that are meaningless, or of little value. It is very simple, my friends. All that is necessary is for you to analyze the thought with respect to the real objectives of your person. If the thought has true consequence, if the thought is of a true developmental nature—that is to say, if it develops either your consciousness or the consciousness of someone else with whom you are communicating—then it is a worthwhile thought. If it does not develop the consciousness, then it is probably of very little value.
Hatonn, in the Maturity Meditation (1972)