Why Some Demons Will not Come Out Why Some Demons Will Not Come Out During a Deliverance Ministry Session During the prayer of deliverance demons do expel through repentance and renunciation prayers. Sometimes they don't for the following reasons: Unbelief (because of hopelessness) Through Fasting Only (Matthew 17:21)* Unforgiveness (a lot of forgiving someone who has hurt you). Self Unforgiveness (living in guilt, shame, or inability to let go of past failures and mistakes.