That is why a musician's imagination naturally dwells on music and musical things, an artist's imagination dwells on artistic things: a thief on how to rob; a writer on the direction he has followed in writing. This is all imagination - that is, it is not controlled by the will. It is this that is the case with the average mind. From morning till evening, the will is actively working on those lines to which the mind has been habituated, the lines which the mind has already formed. For example, consider a person who is always thinking of construction - how to construct a factory, how to build up a certain type of business. During this time he has been forming lines in the area of his mind, or mental being. These lines are open for the imagination, and so the mind goes on working along the same lines which his thought has previously been following, even when he is not specially thinking of those subjects. We still follow the same line we have been thinking on. The line which the will has made in the thoughts are the directions along which the imagination unconsciously travels. "There your heart, there the treasure."