Studying all there is to know about a career without obtaining a degree.

Instead of spending tens of thousands of dollars on a degree; what if a person acquired all the textbooks and materials required to earn said degree (from an accredited college's curriculum), studying it until well versed in all aspects of a career field? If you could prove that you know all the materials necessary to an employer; why couldn't you land a job working in that specific field? Could you pull a "Good Will Hunting" on life and establish yourself into a career without a degree, being completely self educated? Has anybody ever done this to success?