This is a follow on question to Orks Mob Rule in Warhammer 40k. This situation is "No Retreat!" when a fearless unit is defeated in an assault, the fearless unit takes wounds equal to the number their side has lost in combat. I understand so far.
But on p.44 of the WH40K 5th ed rules the last paragraph under "No Retreat!" states:
If none of the enemies involved in the combat against a fearless unit can actually hurt it, the unit does not suffer any wounds if its side is defeated in combat, and simply continues to fight.
If the fearless unit's enemies can't actually hurt the fearless unit, then how did the fearless unit manage to lose the assault in the first place? Are the rules saying any of the fearless unit's enemies still left standing after the assault?