Steiner on clarity of thinking
"No occult teacher will ever instruct a person who is filled with superstition or common prejudice, or one who is prone to senseless judgment or apt to fall prey to any illusion. The golden rule applying here is that, before even taking the first step in the direction of higher learning, a person must free himself from any flighty thinking or possibility to mistake illusion for reality. Above all an aspirant for spiritual enlightenment must be a person of common sense who only devotes himself to disciplined thinking and observations. If a person leans toward prejudice and superstition in the world of sense reality, it soon tends to be corrected by sense reality itself. If, however, a person does not think logically but indulges in fantasies, correction is not so simple. It is essential, therefore, that one have one's thought-life completely in hand and be able to exercise strict control over one's thoughts before ever venturing into soul and spirit worlds. One who easily leans to fantasies, superstitions and illusions is unfit to enter into the schooling prerequisite for spiritual teaching. It would be simple to reiterate that one were free of fantasies, illusion and superstition. But it is easy to deceive oneself here. Freedom from fantasies, illusions, prejudices and superstitions is gained by stern self-discipline. Such freedom is not easily attained by anyone. It must be remembered to what extent most people tend to sloppy, careless thinking and are unable to control their thought life through their own will-power."
Rudolf Steiner. "The Inner Development of Man." New York: Anthroposophic Press, 1970, page 10. Lecture of December 15th, 1904 (GA53). Translated by Maria St. Goar.