Some people ask, "Why do I have a low self-image?"
There are many possible answers that one can give, even though there is only one valid and real answer: "If you have a low self-image, it is because of the way you think about yourself. Think better thoughts and you'll change your self-image."
Thinking of yourself in a consistently negative way is the only way to have a low self-image. Improving your thoughts improves your self-image.
The way you think of yourself now is your present self- image. Regardless of your past self-image, you have free will and the ability to build yourself and your self-image.
(From Rabbi Zelig Pliskin's book: "Building Your Self- image and the Self-image of Others" (Artscroll) Chapter 9)