One of the important things to learn is that the voices in your head are not necessarily you. The modular view of the brain says that different parts of the brain have different responses to things, and some of those parts are involved in generating inner speech.
Once you understand that the voices in your head are not you, you realize you need to judge what they are saying before believing them. Sometimes you must reject them, letting them pass like clouds across the sky of your mind.
One of these voices is the voice of ego. This is the one that boasts or belittles. If you’re doing well, it says you’re the greatest thing since sliced bread; if you’re doing poorly, it says you’re a worthless piece of crap. It is an unfriendly voice, a dangerous voice to listen to. It can make you depressed, sad, and self-destructive.
The voice of conscience, on the other hand, you should listen to. It tells you to be kind, loving, and to care for others. It tells you to treat others as you want to be treated. It tries to get you to act maturely in an immature world.