Low self-image usually forms at an early age. A person might have had excessively critical parents or teachers, failed to get along well with other children, or received low marks in school.
Though this attitude was formed long ago, the only reason it lasts in the present is because a person now keeps repeating it to himself. Yet he has the ability to tell himself, "In the past I may have judged myself to be inferior, but I will now think for myself and appreciate my true value."
Being aware of the source of poor self-image makes it easier to challenge the assumptions upon which it is based. It is possible that while you had certain faults in the past, you presently are learning to overcome them.
Or, perhaps the people who judge you unfavorably were using a yardstick that you do not presently accept. For example, in school a student is usually judged by the marks he receives on tests. Some students with low grades worked hard to understand, and more importantly may have internalized the concepts and practiced them to a greater degree than others who received higher grades. As a child, the diligent student with poor grades might have felt inferior, but as an adult he has the ability to appreciate how he may have really accomplished more.
(Gateway to Happiness, p.129)