People say there is a very small difference between confidence and overconfidence.
- How can knowledge of psychology help someone know whether they are are confident or overconfident?
- What is the state of mind when someone is overconfident?
There are different perspectives that you could take on your question.
An objective perspective could seek to quantify the true probability that a person is correct in their belief. This would be compared with the person's subjective belief that they are correct. Over confidence could then be defined as the situation when the subjective probability is greater than the objective probability. In this objective sense, having absolute confidence removes the possibility of being under-confident, and having absolutely no confidence removes the possibility of being over-confident.
A social perspective could focus on the displays of confidence in an interpersonal setting. In such settings displays of confidence can be used to achieve social goals, such as admiration, access to job opportunities, convincing others to follow a course of action, etc. Furthermore, social norms regarding displays of confidence influence how such displays are perceived. In some situations, a display of confidence may be perceived as arrogance, whereas in others it may be seen as an admirable leadership trait.
The concept of self-efficacy is particularly relevant to your question. It refers to a person's belief that they can succeed on a particular task in a given situation. In general self-efficacy is seen as a good thing. It is associated with self-esteem, persistence on tasks, and many other positive psychological states. However, often there is lack of discrimination between objective efficacy and a person's particular bias in their perception of their efficacy. In some cases accurate self-efficacy leads to better decisions, however in other cases, a slight positive bias may lead to greater persistence and offer psychological protection.
In terms of psychological interventions for increasing accuracy of confidence judgements, the following are some ideas:
Usually, confidence is based on experience; proven results with regards to a task or ability increase one's belief that the task can be completed a second time. Notice that this has nothing to do with what others believe you can do - it's about what you believe you can do.
Overconfidence is bravado - false posturing to fool or mislead others; most often used to hide an actual lack of confidence. This is all about getting others to believe that one is capable of a task.
There are a lot of non-scientific articles related to the difference between the two concepts:
These were found with a Google Search for 'overconfidence vs confidence'. I'm sure you would get more scientific results if you dig some digging, or tried Google Scholar.