Have you ever tried to look at yourself in the mirror and squirmed at your image? If you feel guilty of this habit, then I would recommend you to stop. If you are not contented with yourself, it only shows that you have no self-confidence. If you lack self-confidence, then how do you imagine others to have confidence in you?
Lots of people, old or young, have insecurities about several aspects in their lives. It could be of their physical appearances, speech, lifestyle, behavior, practices, work or even family. Even at interviews, confidence helps you in clinching that job. Consider a situation where two applicants go for the interview where one is confident and certain while the other is an anxious wreck. No rewards for guessing who amazes the interviewer and obtains the job.
Self-confidence is often listed as one of the qualities of effective managers. From your personal experience you can perhaps distinguish the difference between managers with a high level of confidence and those who seem less sure of themselves.
Why then would self-confidence be so nearly related with being effective? It is probably because a persons self-confidence shows confidence in their own decision, and directs others to put their confidence, too, in this judgment. It is also probably because self-confidence is frequently used to overpower the fears, hindrances, opposition and setbacks which can confront the best of plans. People with a high degree of self-confidence are normally more likely to be successful all other aspects being equal than those who work in a less confident manner.