As a metaphor, we can imagine many people wanting to buy apples, but not being willing to pay the 1$ the supermarket will charge. They could create an "apple opening", posting on an apple selling site looking for people who are willing to sell them apples with certain qualities for a given price that depends on the individual, for example 5 cents. Then, we could poll consumers to see how many have apple openings. Perhaps we could find millions of such unfilled openings, but would this tell us anything about trends in the quality of apples or actual apple consumption?