When Ignatius reflected on worldly thoughts, he felt intense pleasure; but when he gave them up out of weariness, he felt dry and depressed. Yet when he thought of living the rigorous sort of life he knew the saints had lived, he not only experienced pleasure when he actually thought about it, but even after he dismissed these thoughts, he still experienced great joy. Yet he did not pay attention to this, nor did he appreciate it until one day, in a moment of insight, he began to marvel at the difference. Then he understood his experience: thoughts of one kind left him sad, the others full of joy. And this was the first time he applied a process of reasoning to his religious experience. Later on, when he began to formulate his spiritual exercises, he used this experience as an illustration to explain the doctrine he taught his disciples on the discernment of spirits.