By recognizing a favorable opinion of yourself, and taking pleasure in it, you in a measure give yourself and your peace of mind into the keeping of another, of whose attitude you can never be certain. You have a new source of doubt and apprehension.

Summary

This quote suggests that when we rely on external validation and approval from others to form our self-image and find happiness, we become vulnerable to their ever-changing opinions. By placing our sense of self-worth in the hands of others, we subject ourselves to doubt and uncertainty, as their attitudes may shift unexpectedly. It implies that true inner peace and confidence should come from within ourselves, rather than relying on external validation.