Here and now
A person lacking in self-confidence who receives a low mark for an assignment may think, "What else could I expect? I'm stupid, this proves it, and I might as well leave." A person with healthy self-esteem who receives a low mark may think, "I wonder where I went wrong? I'll find out so that I can do better next time." Although this person may feel disappointed, s/he does not feel diminished as a person, by the low mark.
If we have little self-confidence then the ‘low mark' scenario may trigger memories of similar events in the past and then lead to a cycle of negative thinking in the form of self-critical put-downs. This is how we intensify and perpetuate a lack confidence. When we feel low like this our expectations about the future tend to be negative and this discourages us from really trying. Then we experience another disappointing result and feel negative about ourselves again.