Why do products sometimes go out of stock?

Products can go out of stock when the store/company does not order enough of the product to sell, or if the product was popular and all of the stock was purchased before the next shipment of the product could come in. As an example, stores work through supply and demand; the supply being the products they sell, and the demand being what the customer wants. When the demand is high but the supply is low the store runs out of their products quickly.