Your business plan will change. Your business beliefs should lead you to long-term success.
Do not spend more time working on your business plan than you do actually working on your business. A business plan is important, and you should take the time to make one. Just know that your beliefs about business will have a much greater impact on your success than what you put on paper.
I know this because I've coached dozens of entrepreneurs and business owners from the very beginnings of their businesses. I've watched some of them grow their businesses all the way to six-, seven- and even eight-figure earnings, even when their initial idea looked shaky on paper. I've watched others struggle for years before giving up, even though their ideas looked foolproof on paper.