"All knowledge that we have, either of the external or internal world, is obtained through only one method - by the concentration of the mind. No knowledge can be had of any science unless we can concentrate our minds upon the subject. The astronomer concentrates his mind through the telescope... and so on. If you want to study your own mind, it will be the same process. You will have to concentrate your mind and turn it back upon itself. The difference in this world between mind and mind is simply the fact of concentration. One, more concentrated than the other, gets more knowledge."

- Swami Vivekananda, "Concentration" (March 16, 1900, Washington Hall, San Francisco)[recorded by Ida Ansell], Lectures and Discourses, Complete Works: Vol 4