When do we need confidence? We need confidence when we are required to speak or to act.
Confidence is generally associated with performing before other people. When I became a waitress I lacked confidence. I could easily serve dinner to my parents and brothers and sisters, but waiting on people in a restaurant was different.
Confidence is also associated with an expectation. This is an expectation we have of ourselves, or that we perceive others have of us. In other words, there is pressure to perform in a certain way.
Confidence cam improve with practice and increased skill. Repeated success builds confidence.