Space Invaders was largely designed and created by one man, Tomohiro Nishikado. He even went so far as to build his own hardware from scratch, as Japanese microcomputers of the time weren’t powerful enough to program and run the game. Even with his specially-designed, pimped-out hardware, the game wouldn’t run the way he envisioned it. The processor just couldn’t make the antagonistic aliens move as fast as Nishikado intended. However, as the player shot more and more aliens, thereby removing entities from the screen, the processer had less and less sprites to render, and the game sped up.

The Effect: That’s right. The way that the aliens moved faster and faster as you thinned their ranks, making the game more difficult as you played? That was a glitch. Nishikado chose to keep this bug in the game instead of trying to compensate for it, because he realized the potential benefits that it could have for the industry (and also his wallet). Other video games of the day would generally be uniformly difficult throughout, and Game Overs just happened when the player ran out of patience or made a dumb mistake. All of that changed which Space Invaders introduced the industry to the concept of a difficulty curve.

This is one of the few innovations that could be considered to have universal influence across all genres of video games (save for purely multiplayer games). Nowadays, any video game worth its salt has a similar difficulty curve. It starts (relatively) easy and gets more difficult as you progress through the game. If the game stays easy the entire time, the player gets bored. Their skills are improving through practice, and if the game doesn’t provide new challenges, it becomes less engaging. The rewarding sense of accomplishment that comes with a finely-tuned difficulty curve is one of the things that made Space Invaders so addictive, turning it into a worldwide sensation (even if it did start as a glitch).