The economics of pinball at its peak, when it took advantage of programmable electronics that would shortly be its downfall.
In 1980, pinball went digital, multi-ball, and multi-media starting with the game Black Knight. Black Knight brought pinball to a new level, literally speaking because it was among the first games with ramps and elevated flippers, but even more importantly because it brought a new challenge that drew in and solidified a pinball crowd. In doing so it also set the pinball market on a path that would eventually lead to its demise.
I remember Black Knight, and reading a story about how it was developed. The voice synthesizer programming had to be tweaked to make the “s” harder, because “I will slay you” was sounding more like an uncomfortable proposition than a challenge. But even then video games were already beginning to displace pinball machines.