Simplicity won
Rivals such as the Atari Lynx and Sega Game Gear had colour screens but their batteries lasted only a few hours. The Game Boy had an unlit monochrome screen and ran for dozens of hours on four batteries. It was designed by Gunpei Yokoi's team with the philosophy of using “withered technology” wisely.
Tetris and Pokémon
In America and Europe the Game Boy came bundled with Tetris by Russian programmer Alexey Pajitnov. In 1996 Pokémon Red and Green launched in Japan and suddenly the link cable made sense: you could trade Pokémon with friends.
Legacy
The Game Boy showed you do not need a TV to play. A straight line runs through the Nintendo DS to the Switch and the Steam Deck.