Self esteem: That is the recognition (by you) that you are worth something. You have a good regard for what you can do. You take pride in doing a job well. You know that you have done it well.
Low self esteem leads to depression and other disorders that are related to low energy, low or no belief in what you can accomplish, and other destructive results like getting entangled in a relationship that is very destructive.
Too high a self esteem makes you very self centered and very selfish. You may even suffer from Narcissistic Disorder. I would google this if you do not know what it is.