You may not need a coach. You may not even be "coachable," i.e., you may already "know everything." However, every top performer globally - from top athletes to the President of the United States - has mentors, coaches, and advisors.
In studies of successful individuals, certain characteristics are always found: They are always goal-oriented, they are always very persistent, and finally, they always have a person or group of persons that they meet with regularly to brainstorm and learn!
Ask yourself: On a scale of 1-100, "how do I perform right now?" If your honest answer is less than 100 - a coach can help you. Period.