Confidence becomes peaceful when proving stops being necessary.

As long as you are proving something, confidence has a job to do and cannot rest. When the proving stops, what remains is quieter: an ordinary sense that you can do what you can do, with no ongoing demonstration required. That state is available and it feels like relief rather than triumph.

Notice who you are still proving yourself to, and whether they are even paying attention. Often it is someone from a long time ago. Recognizing that the audience has left is usually the first step to putting the effort down.