That said Romero's wild-side/recklessness provided the spark that ignited ID software, almost literally if I recall correctly. Basically Carmack had developed a new technology that allowed PC's at the time to handle scrolling. When he showed Romero it at work, Romero basically said "Fuck this company (softdisk), we're starting our own company right now." So starting that weekend they "borrowed" (pretty much stole, but would bring them back each Sunday night) all their workstations and began making a remake of the original Mario game for PC.
So basically, ID software = John Carmack's genius/technology + Romero's recklessness = DOOM.
Highly recommend this book, I don't read as many books as I like but I just couldn't put this one down.