Chapter 11, Macbeth's Mistake, part 3
While they lived, he could not be either. The commandments say, “Thou shalt not covet thy neighbour's goods.” Here was a danger signal. If Macbeth had known as much as Shakespeare knew about the art of sound thinking, he would immediately have said to himself, “ ‘Cawdor' and ‘King' are the roads that I had better not travel along just now, for fear the wheels of my mind should get too much way on, and carry me into danger.” But Macbeth had either not learnt algebra at school, or, if he had, he had only crammed it up for examination out of a textbook, and not learned it as the Science of the Laws of Thought. Another day his imagination showed him a dagger. A dagger is a thing to kill people with. As a soldier, he had probably used a real one in war. But, if he had had any proper nerve training, he would have known that when his imagination was so vivid that he did not, for the moment, know an imaginary dagger from a real one, he ought immediately to “go slack”; to lie down and think about the moors or the sky, or about anything or anybody that was not connected with doing anything in particular, with planning anything, with taking any resolution, and especially with breaking any of the Ten Commandments. He had already told his wife about the three old women. If she had been a sensible woman, she would have told him that she wanted to go away from home; and got him to take her right away for a few weeks; and kept him busy and amused in thinking of other things; till he left off seeing things that were not there. But neither Macbeth nor his wife knew as much as Shakespeare did about the value of danger signals and the conditions for making a safe working hypothesis.
You had better read the story of Macbeth and see for yourselves what they did do. Next to the old Hebrew books, Shakespeare is the best road map that I know of for people who wish to travel safely about the country of the imagination.