First of, thank you very much for taking time in giving such extended help.
Was the encounter with the walls and summons balanced, or relatively so, as a combat encounter for the PCs to fight while the NPC got away?
If so, did the players seem to enjoy that encounter?
If not, did they seem frustrated about the NPC getting away, or about anything else?
It was not balanced at all, but they were in a favourable situation in terms of being able to flee. And they did enjoy the encounter, so much that what was supposed to be a side story is now gonna be a major part of the campaign.
(also, the NPC did not get away, It prevented the party from reaching him)
In what ways did you communicate to the players that attracting attention in the enemy fortress was suicidal? Did you assume it was self-evident? In general, how do you communicate when an enemy is too much for the party to handle?
Regardless of the fortress as a whole, did you communicate the same in the specific instance of the players attacking an enemy, or ask if they were sure?
This particular time, I did not communicate it in any way. But they had an extremely evident chance to study their enemy, something they used to do. I did expect them to take it.
In general, I tend to communicate this sort of things with either abundancy of enemies or by having them gather information about what the enemy is capable of well before facing him.
I'm gonna number the following ones for they are many.
1-Is it possible the players figured they could subdue this particular enemy without raising a general alarm?
2-Have the players ever been in a similar situation before, and did they act differently?
3-Did you have a plan for what would happen if the players were spotted, if they behaved as you expected?
4-If so, why did you not apply it to the situation where they attacked someone in the fortress?
5-If not, why not?
1-I wouldn't say so, but it's not impossible. Particularly, the glass cannon may think he can oneshot people.
2-Kind of, and yes. Two times in similar situations, but more in the open intead of inside a building, they holded their action until they were sure about the enemy numbers and apparent abilities
3-Yes, they could hide in many places or be captured and then get some form of help.
4 and 5- As I said, I take fault in not sticking with what I had planned. I kind of derped out, it was bad DMing. I am making sure that will not happen again, but that's on me. The point of this thread is "how do I let them know that behaviour is stupid", mostly.
6-How common is it for the players to face relatively balanced combat encounters versus situations where they have to avoid combat or flee?
7-How do you handle avoiding combat or fleeing, mechanically? Do you make an effort to make these situations into "encounters" in their own right?
8-How long have you been running sessions for this group?
9-Is this the group's usual playstyle, or a departure from the norm?
10-Before starting the game, did you talk to the players about the tone of the game, what behavior would be expected, and how you would handle dangerous situations and character death?
11-Is it possible that the players are communicating they would like to face more combat encounters they don't have to flee or avoid?
6-most fights are balanced. Occasionally, a fight might be too easy or too hard.
7-when they face someone too strong I always try to have a way out. Maybe they are in narrow corridors and one of them has some form of BFC, maybe the opponent is more interested in doing something else immediately, maybe they happen to be with a convient "red shirt" NPC and it gets caught before them, basically giving them an extra round to react.
8-only a couple of months, but I've been a player in the same group for over a year.
9-in the previous campaign, it was usually me, or another player now off the group, who prevented doing anything without a plan. With the common formation, it's mostly the previous DM who leads the group. His playstyle doesn't seem very consistent, but in sessions with more roleplaying involved everthing went well.
10-no. Do you think it's a good idea to be explicit about this?
11-I don't think so, there have been many balanced fights.
Also,
Teach them what it means to fear.
Yeah, pretty much.