An example about morality and luck.

You don't really need me to explain it – you understand the gist anyway. I won't tell you what and when to take; everyone should choose their own strategy. I'm tired of hearing obvious nonsense about this – this is an example for those who don't understand. You correctly noted that

if the Battle Dice is negative, be prepared for an unexpected loss.

meaning, in this situation, even a 100% chance of success (for each unit) won't outweigh a single instance of bad morale.
By the way, if the damage calculation formula is correct, then based on the attack/defense modifier for a strong unit (against a weak one), luck can add 25% damage, but in reverse – 333% (with weak base damage).