Why does a demand curve slope downwards are there any exceptions?

A demand curve shows the relationship between the price of something and the amount people will buy. The higher the price goes, the less of it you're going to sell. The demand curve has so many exceptions it's basically worthless. It's just a business-school exercise item. Let me throw out an exception: chocolate. Let's say it's August and chocolate's $10 per kilogram, and we're selling all we can make. In September I decide to raise the price to $15 per kilogram. All of a sudden sales of chocolate go UP drastically. Using a demand curve in isolation, sales of chocolate should have gone down. They went up because it's time to start making chocolate Santas. ------------------------------------------------------------------------------------------------- SEPERATE POST The demand curve is not worthless. "The demand curve graphs the relationship between the quantity demanded of a good and it's price, holding constant all other influences on consumers' planned purchases"(Parkin 1.). The example given above is inaccurate as it would not take into account the seasonal demand factors. If these factored in when preparing the demand curve you would find that it true. See; 1. Michael Parkin (1993), 2nd Edition, "Microeconomics". (pgs 73-78)