Nothing remains constant in business: circumstances changes, market change, fashion change, method change.
From the time you must check your sources of information ans reassess your business plan. What is relevant when you start is noy necessarily so in five year's time. You may also need to revise targets and budget s if external factors such as interest rates, vary.
Keep your information up to date and be prepared to change as circumstances demand. A business plan must be felxible not fixed.