DOFF assignment has 2% chance to crit fail. Item has 88% chance to improve quality on upgrade. DOFF assignment crit fails and item doesn't improve.
That is all.
Actually, that's -not- all. This kind of trend is just steps away from a big "F U!" from the game. "All that effort you put into building a decent DOFF deck, all those resources you spent on crafting the Super Double Plus Superior Experimental Upgrade Token, all for naught. I say you lose because I don't want you to progress." Now, obviously, the game itself can't tell me this. That would be silly. But so is the random number generator. Infinity doesn't stop at 12!