Elder Paisios the Athonite. "Words". Vol. 3.
One time, a middle-aged man came to my Hut with a suspicious air about him... From a distance, when I first spotted him, I could tell he was under a demonic influence.
"I came here so you can help me", he said. "Pray for me, because I've been having terrible headaches for a whole year, and doctors can't find what's wrong."
"You've got a demon", I said to him, "because you've given rights to the devil".
"But I didn't do anything!"
"You didn't do anything?" I replied. "Didn't you cheat on a young woman? Well, she went and had a spell put on you. Go and ask her to forgive you, then go to confession, ask to have Exorcisms read over you, and you will regain your health. If you can't perceive your error and don't repent, even if all the spiritual fathers in the world get together and pray for you, the demon won't leave you."
When people like him come to me, with such an air, I speak to them openly. They need to be shaken up in order to come to realization.