* 16 years old Joe buys a $70 cartridge/disc game, already assuming and counting on the $35 that he'll get back on second-hand sell.
That's it. A simple idea that should never cease to be possible, regardless of the medium.
This particular example made games affordable, and it also inadvertently put a concrete price on several other factors like how much it costs to be a first owner vs. wait for a second-hand purchase, and how much it costs to keep it for your collection vs. allowing the product to flow back into the community.