Positive self-esteem improves one's health, sociability and general attitude towards life. Of all the judgments you make in life, few are as important as the one you make about yourself. The difference between low self-esteem and high self-esteem is the difference between passivity and action, between failure and success.
Having a positive self-image is sometimes frowned upon in certain belief systems. Labels such as pride, arrogance, and conceit can sometimes cause us to consciously impose a more negative view of ourselves than is warranted. While arrogance and selfishness should be guarded against, the fear of them should not be an excuse for maintaining or wallowing in low self-esteem.
Negative self-esteem is a habit - a highly addictive habit - and there is little good or worthwhile about having a low opinion of oneself. Habits can be changed.
Books that others have found useful for evaluating, understanding and improving low sef-esteem include:
Breaking the Chain of Low Self-Esteem by Marilyn J. Sorensen and either The Six Pillars of Self-Esteem or How to Raise Your Self-Esteem by Nathaniel Branden.