Once you understand why you were given the promotion or the new position you were given it will bring you into a place of rest. It isn’t because you are “complete” but the potential for growth was spotted in you. You don’t know everything but you have shown you can grow into it.
Greater responsibility is not to be celebrated as an accomplishment but received as a platform to develop your capacity. Continuous learning on the job is therefore the true secret to success. Start and then begin to learn trying new ideas and adjusting until you hit a home run.