The only thing we know about the future is that it will be different.
A question that is often asked in various guises in all kinds of businesses is, how much of this product are we going to sell? The answer is, it depends. It depends on who is asking the question, what product it is being asked about, what the state of the economy will be, what period of time you are looking at, how the product is priced relative to competition, whether there are substitutes available to customers, how the product has been or will be marketed, the product quality, where the product is available, and how quickly it can be provided to the customer.
Demand planning, or just plain forecasting, is what companies do when ...