Quote from ACIM Text Chapter 4, Section 4 - Love without Conflict.

The calm being of God's kingdom, which in your sane mind is perfectly conscious, is ruthlessly banished from the part of the mind the ego rules. The ego is desperate because it opposes literally invincible odds, whether you are asleep or awake. Consider how much vigilance you have been willing to exert to protect your ego, and how little to protect your right mind. Who but the insane would undertake to believe what is not true, and then protect this belief at the cost of truth?