Demand is defined as the quantity of goods that a consumer is willing and able to buy. Willingness and ability are the key factors. I might want a fancy sports car, but I can't afford one. I have no ability to buy. There might be game systems on sale, but I still don't want one. There is no willingness to buy.

In turn, willingness and ability are based on the determinants of demand above. All of consumer demand is driven by these determinants.