Moreover, as long as you are identified with your mind, the ego runs your life, as I pointed out earlier. Because of its phantom nature, and despite elaborate defense mechanisms, the ego is very vulnerable and insecure, and it sees itself as constantly under threat. This, by the way, is the case even if the ego is outwardly very confident. Now remember that an emotion is the body's reaction to your mind. What message is the body receiving continuously from the ego, the false, mind-made self? Danger, I am under threat. And what is the emotion generated by this continuous message? Fear, of course. Fear seems to have many causes. Fear of loss, fear of failure, fear of being hurt, and so on, but ultimately all fear is the ego's fear of death, of annihilation. To the ego, death is always just around the corner. In this mind-identified state, fear of death affects every aspect of your life. For example, even such a seemingly trivial and "normal" thing as the compulsive need to be right in an argument and make the other person wrong—defending the mental position with which you have identified—is due to the fear of death. If you identify with a mental position, then if you are wrong, your mind-based sense of self is seriously threatened with annihilation. So you as the ego cannot afford to be wrong. To be wrong is to die. Wars have been fought over this, and countless relationships have broken down.

Eckhart Tolle

from The Power of Now: A Guide to Spiritual Enlightenment