A childhood belief about computer games

I used to believe that all of the "circuits" (computer chips, etc.) necessary for the operation of a Nintendo game were in the game cartridge, and the console itself was simply an "adapter" that enables the game to fit into the input jack on the TV. (this was back when video games came on those weird shaped cartridges, not CDs). I wondered why they didn't redesign the game cartridges so that the part you plug in will fit into the input jack, because then you wouldn't need the console and it would save money. To solve this problem I later reasoned that there were "common circuits" that all games needed, and these were in the console, but there were other "circuits" that were specific to each game, which were on the cartridge. Later, of course, I found out that all the "circuits" are in the console, and the cartridge is just a data storage medium.