At over 118 million units sold worldwide, the Game Boy is the third best-selling game system of all time behind the PlayStation 2 and the Nintendo DS. It's certainly one of the longest-lived game systems ever released: The Pokemon boom of the late '90s was a veritable dip in the Fountain of Youth for the hard-working handheld. Nintendo eventually improved on the Game Boy with the (smaller, lighter) Game Boy Pocket and the Game Boy Color, but when gamers think "Game Boy," they generally think of the good old "grey brick" that simply wouldn't die. Even Sega's increasingly savage attempts to make the Game Boy seem uncool next to its own portable Game Gear did nothing to slow the Game Boy's momentum.
In the end, the Game Boy's sales lapped the Game Gear's comparatively modest numbers. There's no hard data on how many units the Game Gear sold (between 10 and 11 million is the popular estimate), but it's safe to say the Game Boy performed far more admirably. Given how the '90s were all about Sega dunking on Nintendo for being behind the times, it must've vexed Sega of America's talented marketing team to see its proven tactics prove utterly ineffective. In fact, the Game Boy succeeded because it was behind the times, which probably proved especially dizzying to said marketing team. Sega's "Genesis Does What Nintendon't" and "Welcome to the Next Level" campaigns leaned heavily on the power of the Genesis next to the NES and the newborn SNES. The Game Gear ads tried a repeat attack, but fans who adopted Sega's portable quickly learned power isn't an asset for a handheld when six double-A batteries are required to run said handheld for half an hour.