How can there be a bad flash?

…maybe there’s something I don’t know, but it sounds a little bit silly to say “my drive was flashed badly, results of burning show it, I have to reflash my drive…”.
I mean, either it is flashed good and it’s working or the device won’t work. It’s digital, two discrete states. If there was something like that with flashing MoBo’s there would be hell of a lot of dead computers just because “it wouldn’t settle itself well on eprom for no reason”.
Can anyone explain mentioned phenomenon?
I tried to use search, but it’s not working…at least here :frowning: