Clearly people like to feel smart and appreciated and accepted by others. Any affirmation of an opinion, compliment, or otherwise encouraging or appreciatory statement is a natural boost to one's sense of self image. It just makes you feel good to hear that you are.
Conversely, negative statements, "What do you think you're doing ?", "You are a big loser", or "You couldn't pull that off if your life depended on it" only serve to pull us down because they make us question our abilities and tax our sense of self worth.
In the end positive statements and encouragement help. Negative, disparaging remarks don't. It is that simple!