How you think of yourself and what you believe about you was built into your thinking as you grew up.  Very early on, your self esteem was established by the thoughts and opinions you received from others, usually parents or other caretakers.  Most nurturing caregivers help a child to gain self confidence and to believe in him or herself.  Sometimes though, the job of instilling self esteem falls short.  It could be for many reasons.  Maybe the family moved a lot, perhaps the caretakers were not in the best of health.  Any event or condition like that could take the focus off of what could be best for a young person.  Because of these circumstances, how you feel about yourself may have ended up being on  the low end.  

Part of being human includes having doubts about yourself.  It is very common to feel like you are on a lower level than someone else (which is not true, by the way).  This negative thinking is a part of low self esteem.  If you allow this negative information to take root, it could cause some serious problems for you down the road.  Perhaps it already has.  But it is not too late to do something about it.  

There are ways to deal with this lack of self confidence and to get rid of the negative emotions.  There are plenty of self help books that can teach you new ways of thinking that will help you overcome self confidence issues.  Try listening to some self development CDs in your car on the way to work.  You have to sit in traffic anyway, you may as well be learning something.  Counseling can also work wonders.  A good counselor can assist you in finding the root of your negativity about yourself and begin to heal that.  

The most important part of any method is to be consistent.  Once you start, follow through because old habits and thought patterns can be difficult to break.  Toss those items out, such as the "I can't" or "I'm stupid."  A popular one is to blame your childhood.  Well, you are not responsible for the way you grew up.  But, you are responsible now and you have the power to take back your self esteem.  If you improve the way you think you will improve every aspect of your life, including your self confidence.  

The best method is to replace the negative self talk with more positive affirmations.  Always tell yourself you can, you ARE smart enough and qualified enough for that promotion, you have talents and abilities just like everyone does.  You can and will pull yourself up from your circumstances and you have as much of a chance to do that as others do.  Changing your thinking, and giving yourself positive messages on a daily basis will drastically improve your self esteem.  Take it back now, it's not too late.