That is a great thing to make sure you have in your business plan, that your business will be built around those real customer wants. Do not make callous assumptions, or statements like "I know what people want", "People are going to love this", and so on. Have you done your research? Do you really know that the people you will be targeting want your product / service, and crucially do they want it AT THE PRICE that you will be offering it at? Whilst confidence in your plan is fantastic, you must make sure that it does not lead you down a blind alley along a path that is not desired by your target market. Don't assume what customers want, do your research and make sure that is clear from the start in your business plan.
But your fixed expenses don't do this. They remain the same no matter what sales does. That's why it's call fixed. These are expenses like rent, taxes, utilities, phone, salaries, insurance, etc. A lot of business owners never consider this. They just lump all their expenses together. But you could never make an accurate plan if you combine all your expenses together. If you project your sales higher and want to know what your expenses will be, you have to separate your fixed and variable. So, thinking about this principle, let me ask you a question. If your sales grew 10% and nothing else changed, would your profit margin be higher, the same, or less? Profit margin is % of profit against sales