People with low self-esteem are frequently very good people by objective standards, but have high aspirations and hence feel frustrated in not reaching their lofty goals. Since they are not perfect, they consider themselves failures and this leads to many negative consequences.
It is important for such people to realize they are thinking in either/or terms: "Either I am perfect, or else I am a failure."
In truth, each area of behavior and personality has numerous levels along a continuum. If you are not perfect, you need not rate yourself as a failure. Focus on improvement, instead of absolute perfection.
It is worthwhile for a person with low self-esteem to write a list of the minimum standards of a basically good person. He is then able to see more objectively whether or not he is meeting those standards.
(Rabbi Pliskin's Gateway to Happiness, p.132)