“Sometimes the thought of my sins causes me great sorrow; sometimes Satan desires to make me sad on account of my tepidity and heaviness of soul; for my joy torments him and he envies me the graces I have received from God. I know also and see that if the devils cannot hurt me in myself, they try to hurt me through my Brethren, by endeavoring to extinguish holy joy in their hearts. But if they cannot injure me or my Brethren, they retire in great confusion. When, therefore, I am tempted to sadness and bitterness, I consider the joy of my Brethren, and the sight of their happiness and cheerfulness drives away my heaviness and sadness, so that I am excited to interior rejoicing and exterior cheerfulness.”
St. Francis of Assisi  (Pg. 229 From “Works of the Seraphic Father St. Francis of Assisi”, translated by a religious of that order. Imprimatur: William Bernard, Bishop of Birmingham)