As with everything else, there's a lot of
Common knowledge: Doom killed the amiga
Why it's wrong: Doom was released in December of 93. Commodore declared bankruptcy in April 94. There's plain not enough time for an entire platform to go from doing well to dying off, based on one game in about 4 months. (Doom was massively important in fuelling the PC as a valid games platform, but that's an entirely different story)
I won't speculate on what killed Commodore the company. BUT I have to tell you that for my friends and I who had Amiga 500s at the time, DOOM was definitely the thing that made us (I had about 7 friends with Amiga 500s) switch from playing on the old 500s to the PC. Before that, the PC was just a boring work box. DOOM and all the 3D games that followed were the reason that I bought tons of video boards, CPUs and RAM for my PC and why my Amiga sat in the closet until last year. Just telling you what happened from my perspective (in my early 20s at the time), because I lived it.