The adults who seem certain mostly just got used to being unsure.

Confidence is less often knowledge than tolerance. People who have been deciding things for twenty years do not have better information; they have stopped needing the discomfort to go away before they act. From outside that looks like certainty. From inside it is a familiar unease they no longer treat as a stop sign.

Next time you are waiting to feel sure, notice that you may be waiting for something that never arrives. Act on the best read you have and keep the decision small enough to adjust. The unsure feeling stays, and that is normal.