We are wrestling with an enemy that has already been defeated. If you do not know the enemy is defeated, he can fool you.
 
This applies to every circumstance. You must always see a defeated enemy.
 
David’s courage came from asking: "who is this uncircumcised philistine who defied the armies of the living God?". He knew that because they had the covenant, if God is on their side, nothing—whether disease, depression, or a bad habit—can be against them (Romans 8:31). 
 
The victory is secured; your job is to perceive it.