Most of us have a negative thought process operating just below the surface of the mind. It is name-calling (e.g. "I'm not good enough," or "I'm a loser"). I characterize this thought process as the Critic.
From below the surface, the Critic is verbally attacking you. You are generally not aware of the particular language, but only its effects...moods, reactions, attitudes, insecurities. The Critic can cause you to feel depressed, guilty, irritated, judgmental, inhibited, unworthy, unappreciated, inferior, undesirable...the list goes on and on. You experience the effects without recognizing the cause.
Parts I and II of the book give a clear picture of how the Critic operates. Part III helps you to recognize it in the moment, and Part IV gives you the strategy to reduce and eventually stop it.