Confidence increases productivity and causes you to choose more challenging tasks, which make you stand out amongst your peers. You naturally create a more cohesive workplace environment; confident people celebrate the accomplishments of others as opposed to insecure individuals who try to steal the spotlight and criticize others in order to prove their worth. Speaking first and often (a sign of high self-esteem) makes others perceive you as a leader. In fact, over-confident people are more likely to be promoted than those who have actually accomplished more.