A professional athlete would no more attempt to achieve their best game without a coach than without the kit to perform in. Indeed, running around naked would be less of an embarrassment than having the raw potential to achieve great things but fail to make it because of a lack of appropriate and effective coaching.
It is the same in business. Those who recognise the potential in themselves or in those they employ hire a coach. it's not just a good thing to do, it's an essential thing to do. the alternative is to anticipate and accept a lower standard of performance than a person is capable of giving.
Only the deluded or fearful try and take on the world alone