Christians know that their enemy the devil prowls around like a roaring lion looking for someone to devour. (1 Peter 5:8) That "The Thief", another name for our enemy, comes only to steal, kill, and destroy. (John 10:10) A good example of how Satan tries to do this is found in the account of the Temptation of Christ - Matthew 4:1-11.
Temptation has at it's core doubt in something or someone. The challenge to turn the stones into bread doubted God's Provision. The dare to jump from the top of the Temple doubted God's Protection. The invitation to worship Satan for all the earthly kingdoms doubted God's Promises in Christ. In addition, all of the tempting was targeted at two vulnerable points - (1) when Christ was alone and (2) at Christ's supposed weaknesses.
The Spirit led Jesus into the wilderness to experience these temptations and possibly other trials during His forty day fast, on our behalf. The Word of God, which was Himself in the flesh, now physically responded to each temptation by declaring the truth of the matter. The answer always was and is the same - "It is written....".
"It is written..." must be the Christian's war cry also. Our foundation, our source, our sustaining force must be The Belt of Truth that holds everything together and upon which all the weapons of warfare hang. Christ Jesus is the way, The Truth and the life. All power to destroy the enemy's attacks, temptations or otherwise, is found in God's Word and thwarted by verbalizing "It is written...".
It is a good thing to sure-up the areas in our life we know are weak and guard, with God's help, against temptation. However, I encourage all of us - should we find ourselves alone and our weak points being targeted with temptations by the enemy - the answer is always the same and always available - in God's Word, research it, read it, and recite it. Whatever "it" is, the start of resisting the devil and seeing him flee is declaring "It Is Written...".