In The Confidence Code: The Science and Art of Self-Assurance—What Women Should Know, Katty Kay and Claire Shipman attempt to define confidence, to determine how it is developed, and to give guidelines for developing it. Without confidence, you lack boldness and faith in your abilities, and this dearth can greatly affect your mental health as well as your career success. Low confidence can make women appear incompetent.

Their premise is that confidence is "in alarmingly short supply" for women. Why women in particular? Some bigots suggest that women are biologically inferior, others insist that children change women's priorities so that careers, and the confidence that comes with doing a job well, are not important. Others blame the cultural, social, and institutional barriers set against women's success.

Kay and Shipman acknowledge that there is some truth in the latter two reasons but point out that the main reason women have lower confidence levels is because they tend to lack self-belief. The authors find that women need to stop worrying about failure, second-guessing, and to put less emphasis on how others might perceive them. Women need to stop worrying that they cannot succeed but instead start taking action and risking failure. By not believing that you can succeed, you are less likely to even try.