There are times when a counselee seems to be unable to overcome a sin issue even though they have learned the truth and understand the truth.  This is always puzzling to me as a counselor because I have complete confidence in the Word of God to address every problem of life.  
I am not one to support the saying of “the devil made me do it” but as a believer in all that the Bible has to say I do not deny the reality that there is an invisible realm in which the forces of good and evil exist. It is in this realm that spiritual warfare takes place for Kingdoms and countries. It is in the human heart that spiritual warfare takes place in the Christian’s life.
For though we walk in the flesh, we do not war according to the flesh, for the weapons of our warfare are not of the flesh, but divinely powerful for the destruction of fortresses. 2 Corinthians 10:3-4 (NASB)
What does it mean when a counselee is seemingly unable to overcome a sin habit such as anger, or using pornography, or swearing? It is spiritual warfare?
The reality is the Believer is always involved in spiritual warfare! Our flesh is strong and is made stronger as we are influenced by the world and cooperate with the Devil as he operates in this sphere. The Spirit of God indwells the regenerated person as well and this sets up an ongoing battle in the heart and mind of each of us. The battle is evidence of a changed life for there is no conflict in the inner man of the unregenerate heart.
For the flesh sets its desire against the Spirit, and the Spirit against the flesh; for these are in opposition to one another, so that you may not do the things that you please. Galatians 5:17 (NASB)
Many are fooled into believing they have no control over their actions; that they are incapable of staying away from pornography or exploding in anger or swearing. This is self-deception and excuse making at its finest. It is so much easier to shift the blame for sinful behavior over to the Devil than it is to take responsibility for your actions, isn’t it?
Note what Paul says at the end of Galatians 5:17, “so that you may not do the things that you please.”
 This goes hand in glove with what is said elsewhere in Scripture
…lay aside the old self, which is being corrupted in accordance with the lusts of deceit… Ephesians 4:22b (NASB)
…make no provision for the flesh in regard to its lusts. Romans 13:14b (NASB)
Therefore do not let sin reign in your mortal body so that you obey its lusts, and do not go on presenting the members of your body to sin as instruments of unrighteousness  Romans 6:12,13 (NASB)
“Lust” is the result of what a person thinks about, and desires (longs for) in their heart.  As the lusts are indulged over and over the sinful thoughts and responses become a pattern of life, and a part of their normal behavior. Angry responses and other sinful actions become automatic behaviors that are default positions for the individual. A person who has a difficult time overcoming a sinful habit is most likely giving themselves permission to act in that same sinful pattern. 
While there are occasions when the person is conscious of granting themselves permission to act sinfully, many counselee’s report that it “just happens” before they realize it.
The key to overcoming these kinds of sinful automatic behaviors is to admit the real problem is not the behavior you exhibit, but the heart issues behind that behavior. What motivates the sin is in the heart and that is where the first change has to occur.