Sleep
Be alert! If you have stood on guard for six nights, without a smell of the enemy, you become complacent and victorious. You fall asleep. Now they attack!
It will be good for those servants whose master finds them ready, even if he comes in the second or third watch of the night. If the owner of the house had known at what hour the thief was coming, he would not have let his house be broken into. Luke 12:36
Never underestimate the power of delusion. It is the most cunning of enemies. Also, never forget what the enemy looks like! It is so easy to let the enemy through your doors thinking them to be a friend.