How many different forecasts do you think the retailer had to make in order to decide how much product to stock?

Think of a product you have recently purchased. How many different
forecasts do you think the retailer had to make in order to decide
how much product to stock? What are the consequences for that
particular retailer if they had over-forecast versus under-forecast?
Write 250 words. This forecasting is not weather related, its about
logistics.