An XP practice. There's a tendency when an EngineeringTask starts to go bad for the developers to feel embarrassed and to stop communicating about it. They stop checking in work and stop talking to people. Flow is diminished.
Therefore,DontDoThat. Keep everyone clued in. No-one will blame you if you strike a thorny bit, and truly this is just the time when everyone should get a chance to help you. Stay connected to the group and keep 'em clued in.