“One simple method is to take a pen or pencil and hold it up against a blank wall or ceiling. Now concentrate on the pen as if it is the most important thing in the world. Then allow your sense to relax, so you see the pen against the background of the wall. Concentrate again. Relax again. Keep on doing this until you become aware of the ability to focus attention at will. You will find that this unaccustomed activity of the will is tiring; it produces a sense of strain behind the eyes. My own perception is that if you persist, in spite of the strain, the result is acute discomfort, followed by a sudden immense relief - the 'peak experience.”

Source: Access to Inner Worlds (1990), p. 33