Morale

You usually makes a morale check under three conditions, when your side of an encounter has lost a member due to death or desertion, When you lose half your vitality, or when half the group on your side is either killed or otherwise incapacitated. You are at -1 for every member of your side you lost in the past minute.

From https://geek-related.com/2012/04/14/morale-in-dd/

In fact, I think morale can be improved. Back in my Animals in D&D article I proposed to split morale into two factors – one which determines how likely something is to attack in the first place, an aggression value – and one which determines how likely something is to keep fighting. This is especially great for animals – unlike in computer games, animals usually don’t just attack for grins. And some will flee if they get hit once, while others won’t. Heck, it’s good for NPCs too – I remember as a new GM back in AD&D 1e days being confused in T1 the Village of Hommlett as to whether the berserkers in the gatehouse were just going to attack anyone they saw, or what? They’re berserkers, but on the other hand they seem to just be chilling in a building with other kinds of creature around…

Sure, if you plan out every single encounter and what is “supposed” to happen you might not need the aggression. But many of us use random encounters, and also have just stuff out there people can wander across – is that owlbear feeling very irate, or just standoffish today?

So I’m definitely in favor of morale coming back. Let’s say convert it to a d20 roll as is more traditional now. First value, roll over to attack, second value, roll over to keep attacking. And you get a bunch of more interesting behaviors quickly defined…
 * Morale DC 20/10: isn’t going to attack unprovoked, will bail about half the time if it’s in a fight that’s not going well (most animals might fit in here.)
 * Morale DC 10/0: Somewhat likely to attack you, but once the fight starts there’s no going back! Maybe a good value for those berserkers in T1.
 * Morale DC 20/20: Not gonna fight, always gonna run, like a peasant or small herbivore or my dog.
 * Morale DC 10/0: Going to attack half the time, will never flee or surrender
 * Morale DC 7/15: Likely to attack, but not likely to stick with it (many ambush predator types fit into this category, like my cat)
 * Morale DC 5/5: Aggressive and elite critter
 * Morale DC 0/0: Stone golem, crush them!