Pong

The original arcade duel. Move your paddle to rally past the CPU — first to seven points wins.

Pong was not the first video game but it was the first commercial success, and it exists because Bushnell set it as a training exercise for Al Alcorn in 1972. The first cabinet, in a Sunnyvale bar, famously stopped working because the coin box had jammed completely full.

It also contains one of gaming's earliest deliberate design frictions: the ball speeds up as a rally continues, and the paddle is divided into segments that return different angles. Neither is realistic physics. Both exist to stop two competent players rallying forever, which is the problem every symmetrical game has to solve somehow.