Stop performing certainty and develop capability.

Performing certainty is a substitute for having it, and the performance takes energy that could have gone into the underlying skill. It also traps you: once you have projected confidence, admitting a gap becomes costly, so the gap stays. Building actual capability solves the problem the performance was covering.

Identify one place where you are acting more sure than you are. Instead of maintaining the act, put a few hours into genuinely learning the thing. The relief of not having to perform is worth the effort by itself.