Who did it: Sega
A blunder so bad, you're left wondering, "What was Sega thinking?"
Following a string of poorly conceived add-ons (ahem..Sega CD and 3DX), the Saturn looked to be the salvation for the company that once went toe-to-toe with Nintendo.
Sure, Sony looked like it could potentially be a threat with their at-the-time upcoming Playstation console, but people knew Sega. It was a brand they could trust. Or so they thought. Originally scheduled for Saturday (er, "Saturnday), September 2nd, 1995, then Sega of America President, Tom Kalinske, recanted those statements and said that the system was to come out immediately.
The move backfired terribly (it cost $100 more than the Playstation, companies like Walmart and KB Toys weren't even included in the early launch, and most didn't even know the system came out), and it basically ruined the trajectory of the system's sales. Sega would ultimately release the beloved Dreamcast a few years later, but the damage had already been done with the Saturn. Sega never recovered and later had to leave the console business altogether. Shame, too, because the Saturn was one hell of a system.