Billionaire technology entrepreneur says that learning supply and demand as a 12-year-old selling stamps was a valuable lesson in business.

Now the 78-year-old collector serves as director of the Cuban Philatelic Society of America, a nonprofit organization dedicated to the study and collection of stamps from Cuba and other countries.

Mark Cuban was a hustler at a young age, selling items like trash bags, baseball cards and stamps door to door. ... How 12-Year-Old Mark Cuban Developed Tough Skin To Reach Billionaire Status.

This year's World Stamp Show had plenty of examples from the developing world. For Pakistan, stamps symbolized independence. In Cuba, they celebrate the health system.