When we’re designing non-player characters (NPCs), factions, or cities, we have to consider how they would respond to the various actions that the party might take. Thankfully, humans have 4 predictable responses to almost every scenario that they encounter, and it can be linked to the familiar fight or flight response.
There’s a part in our brain, called the amygdala, that we use to determine if what we’re seeing is dangerous. It quickly assesses if we should fight, flight (run), if we could socialize, and finally we freeze if we do not have enough information. This is the cause of the deer in headlights: because they have not evolved with experience to know what a car is, they freeze like a computer which cannot compute due to insufficient data.
With these, we can consider the response that our NPCs or social groups would have to our party. Consider this for literally every single case because this is precisely what will ensure players agency in the game; it ensures that players always have a choice to make in how they play, and ultimately contribute to the story.
Fight
“What happens if the party were to attack them?”
When we have an NPC or city in mind, we should immediately consider how would they respond if the party were to attack them. In the worse case, what would be the consequence if the party killed this character? It will be tempting in some cases to think that there is no way that the players would want to fight or take issue with the character, but that is precisely why we must consider it. Giving thought to the most violent respond is what will give scope and depth to the choices that the players have, and will also prepare you for anything they might do.
In the extreme case, consider how the story and plot would continue if this NPC were killed. No character should have plot armor, which would keep them immortal until a desirable plot point takes place. Consider alternative options and you will likely love the surprising events that can occur.
Flight
“What is the characters goal before meeting the party?”
Opposite of fight, sometimes the players feel the best decision is to turn and run away as fast as they can, or do everything they can to avoid the character or scenario that you are proposing. This might be frustrating because you have put a lot of thought into it, but just like the potential death of the character, you must consider what would happen if the players did their best to avoid the encounter all together. What is the characters goal before meeting the party?
Consider what the NPC is looking to do anyway, outside of the parties intentions and story. Characters should have their own goals and motivations, ones which they would want to pursue without the parties interruption.
Freeze
“What would they do if the party does nothing?”
This can be very similar to analysis paralysis. Effectively, this is doing nothing. Consider what the NPC would do if the players literally sit in silence, not responding or knowing what to do. You may need to provide more information, allude to some historical knowledge, or just have the NPC carry on their tasks. In any case, think about and plan for the event in which the players don’t know what to do. This may have some similarities to the flight response, most likely depending on if the characters encounter one another.
You can also honk the horn! Sometimes the answer could clearly be that the NPC intends to hurt the party. If they freeze, perfect time to attack! Ultimately, consider the NPCs interests and motivation: what do they see before them? What is their response? They might even freeze too, creating the lovely awkward silence! At length, what happens if the party does nothing?
Friend
“What would it take for them to be allies?”
We are social creatures and it is in our benefit to try to befriend those around us, and animals too! Players might surprise you with what they want to try to be friends with. You might think that the lich who has been killing and enslaving people for years would be immediately met with violence or fear, but what if the players want to know more about them? What if they want to try to understand the NPC’s motivation? It could lead to compassion, which could lead to understanding and friendship. Of course, it may not be possible in some circumstances, but it is always good to consider how they would react if the players ask, “I wonder if we can be friends with them..?” or “What is it that they really want..?”
For more information about the amygdala, please consider this video:
Mym's Well 
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