What you master in one area does not make you adept at other similar areas.
Writers are good at putting words on papers but may be clumsy at public speaking.
Interior designers are skillful at architectural aesthetics but may be bad at designing book covers.
Self-help gurus who preach the guides to build good habits but may find it difficult to keep bad habits at bay themselves.
Be careful with what you expect with your knowledge. Getting an MBA does not mean you can run a business. Reading a fitness book does not make you fit.