" When he thought of worldly matters, he found much delight; but after growing weary and dismissing them, he found that he was dry and unhappy. But when he thought of going barefoot to Jerusalem and eating nothing but herbs and of imitating the saints in all the austerities they practiced, he not only found consolation in these thoughts, but even after they had left him he remained happy and joyful. He did not consider nor did he stop to examine this difference until one day his eyes were partially opened, and he began to wonder at this difference and to reflect upon it. From experience he knew that some thoughts left him sad while others made him happy, and little by little he came to perceive the different spirits that were moving him; one coming from the devil, the other coming from God. "

― Ignatius of Loyola , The Autobiography of St. Ignatius