Sales data versus consumption data
A product has 3 major stages in its lifecycle: production, sales, and consumption. A company does not produce 1 million bottles of something if it not sure that it will be able to sell them. In other words, no one would imply sales from production: they are seen as totally independent numbers. Likewise, a company should not sell the same 1 million bottles of its product unless it plans those to be consumed. Yet: that does not happen: companies imply that because they sold a product, it will of course be consumed. So, whereas no one considers that there is connection between production and sales, the same does not happen between sales and consumption. The end result is that, if 500 thousand consumers do not consume the product, they will not buy it again, so when the company produces again 1 million bottles based only on sales data, it will find out that it is only selling half of the production and will not understand why. Consumption data assures the NEXT sales, and companies which do not understand that will see their market share eventually disappear.