"The collector is in reality the stamp market. It is he, for whatever irrational reasons, who buys this otherwise worthless piece of paper and puts it in an album never to sell it until dotage or death. One group of market analysts watches the larger stamp dealers, who sell primarily to collectors, to see what they have in short supply-- for it is collector demand that has pruned these dealers' supply. Such items usually go up in price. Theories on how much a particular item will go up once it has begun its move abound; unfortunately, they do not predict much better than chance."
From The World of Stamps & Stamp Collecting by David Lidman and John D. Apfelbaum
Published 1981 by Charles Scribner's Sons