1. Partnership with Sony
Okay, so Nintendo didn’t really make the PlayStation on Sony’s behalf and hand it to them on a silver platter, but they were working together to create a CD-ROM device for the Super Famicom (god, I wish we could have seen that; it probably would have made this list). The partnership was broken when the two entities couldn’t come to a suitable revenue sharing agreement (let’s face it; Nintendo was just greedy).
And, let’s be fair, had Nintendo kept their partnership with Sony, they may not have had to compete with the PlayStation or the PS2. The events described here were really the catalyst to the formation of Sony Computer Entertainment and ultimately the PlayStation consoles. Go figure.