What is effectual demand, and why is simply wanting a product not enough to create an effectual demand for it?

Effectual Demand, can be explained as the demand followed up with at least just the right willingness to pay to bring the products or services demanded into the market.

Simply wanting a product is not enough to create an effectual demand for it because Effectual demand is shows the extent to which the income of the buyers, his perceptions and needs can be combined to result in an actual purchase and not just the mere desire to purchase.