A lot of people don't feel confident at work. They may be in jobs that require skills they don't exactly have. Some don't have as much experience as their peers. Some are simply new to their jobs and feel like they might not measure up, that colleagues are a threat to their job security, or that they might lose their job. In many cases, these people are being too hard on themselves, but there are a few more serious reasons to lack confidence at work.
On the job harassment by coworkers or publicly making serious mistakes can make it a lot more difficult to keep your spirits up. So can being forced to work with people you don't feel comfortable being around, or those who make you angry. One of the most common reasons to lose confidence at work is a bad relationship with your boss. Even though these reasons can be difficult to overcome, there are ways to improve your at-work confidence.
One is simply to be more assertive. It's easy to feel like others will consider you too pushy, but assertiveness often gets the job done. The more you act as though you have confidence, the more you're likely to get results that will boost your self-esteem. Remain focused on your work and your job, instead of allowing yourself to be brought down by the behaviour of others. Identify what you do best and what you're not great at and work to emphasise your strengths and decrease your weaknesses. Above all, trust your instincts; you can do valuable work and be an asset to your company, even through adversity.