Watch and Pray:

Watch yourself with all diligence, lest the enemy steals near and robs you, depriving you of this great treasure, which is inner peace and stillness of soul. The enemy strives to destroy the peace of the soul, because he knows that when the soul is in turmoil it is more easily lead to evil. But you must guard your peace... An advance of the enemy is a self-reliant thought. Make it a rule to guard as clearly coming from the enemy every thought which tends to decrease your conviction that all good comes from God, that you can succeed in nothing without the help of His grace.

St. Nicodemus the Hagiorite and Lorenzo Scupiloli. Unseen Warefare, Chapter 23, p.271