Who wants to go back to square one on your project when you are so closed to the finish line?
The bug that was just found will prevent any customer from upgrading.
Or it will erase their data.
Or support will not be able to diagnose issues as they did before.
Take your pick, ITS THAT BUG, the one that you have a meeting about to discuss with everyone in the room and is currently keeping you up at night.
And it’s forcing you to go back into the core to fix it and subsequently revalidate all of your development up until now.
That’s a bad bug.
At this point you can deal in workarounds (technical debt anyone?) or you can go back to the beginning, back where’s happening, start over and fix it.
Not an easy choice to make, but said anything was easy.