“Who knows who is producing the changes in the minds of men today, producing war or peace. It could be some woman treading in the winepress; or – as Yeats said – it could be in the mind of some shepherd boy, lighting up his eyes for a moment before he ran upon his way. Dreaming of heroism, of noble battles where he was the hero, that little boy can cause the blood to flow. If you know who you are and how imagination operates, you will learn to control your imaginal activities. If you do not, they will be controlled for you by another, and you will become their victim.”
Source: THE SECRET OF CAUSATION