Battle for the Mind

In the Christian culture, there is this idea that one battles for their mind, heart, and soul against a prince of darkness. This personified essence is one who comes to lie, kill, and destroy. However, what if in reality that prince of darkness is you? You're the one you're battling against for control of your mind, heart, and soul. What does one do with that? How would you proceed in battle when you know your enemy knows all your best moves and can outplay you?