Confidence follows evidence

Confidence is not a feeling you generate before acting. It is what accumulates after you have done something a few times and it went acceptably.

Which means the advice to "just be confident" is empty. You cannot decide to feel certain about something you have never done. What you can do is act before the feeling arrives, survive it, and let the feeling catch up.

The order is: act, then feel. Most people wait for the reverse and wait a long time.

Competence is the foundation, and it is the part people skip. Someone who knows their subject has a steadier floor than someone using technique to appear assured. If you consistently feel unsure in one area, the honest question is whether you actually know it well enough, and if not, that is fixable in a way that pretending is not.

Distinguish nervousness from unpreparedness. Nervous before a presentation you know cold is normal and passes. Nervous because you have not thought it through is information, and the fix is an hour of work rather than a breathing exercise.

Nobody is watching you as closely as you think. In any meeting, most people are thinking about their own contribution. The mistake you replayed for three days was noticed by almost nobody and remembered by no one.

And confidence is not volume. The most credible person in a room is often quiet and specific. Loud certainty is easy to produce and people learn to discount it.