So what happens when you write a seriously hard to solve bug or you accidentally misarchitected your internal framework in some fundamental way that wasn't clea

So what happens when you write a seriously hard to solve bug or you accidentally misarchitected your internal framework in some fundamental way that wasn't clearly obvious until you're too far down that path to fix it? What do you do when the 1 to 10 of you that "own it" aren't smart enough to figure it out? What happens if that mistake is time sensitive or extremely costly?