Most of the best-selling games on a platform are the system sellers. But in same cases, they're just a really popular second or third choice for someone getting the biggest system seller.
Atari 2600: Space Invaders. I don't think Atari consoles or consoles in general would've taken off without it.
NES/Famicom: Super Mario Bros./Duck Hunt. We all know it.
Game Boy: Pokemon Red/Blue/Green. The Game Boy was already very successful, but this massive new IP saved it from irrelevance and also drove people to get Game Boy Color for other Pokemon games.
SNES/Famicom: Super Mario World. After Sega flexed their graphical muscles by beating the SNES to the market, Super Mario World proved Nintendo was still in the game.
PS1: Gran Turismo & Final Fantasy VII. Gran Turismo outsold FF7 by about 800k but they both sold 10 million (under 11 million). Gran Turismo was the first-party game that truly proved Sony's dominance and FF7 was the third-party exclusive that killed the N64's chances of matching or exceeding PS1 in sales.
Xbox: Halo: Combat Evolved. Halo 2 may have sold more, but it was because it was building on the hype of CE. Halo CE was the killer app that made people get an Xbox either in lieu of the other consoles or in addition to them.
Lifetime Sales Predictions
Switch: 161 million (was 73 million, then 96 million, then 113 million, then 125 million, then 144 million, then 151 million, then 156 million)
PS5: 115 million (was 105 million) Xbox Series S/X: 48 million (was 60 million, then 67 million, then 57 million)
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima
