Businesses are often started by aspiring entrepreneurs who have excelled in previous jobs with exemplary skills. For example, a great engineer might decide to start a business manufacturing innovative machines for a niche he is familiar with. Or a great salesman might start a business marketing products in a business to business venture. Rarely do business owners have formal training and experience in all facets of managing a business. They learn it on the job.
Consultants are brought in fill in the gaps when a business owner ventures outside his or her core competencies.