"So you're telling me that a combat encounter is a function of the mental state of the PCs." Well, yeah. A function of the mental states of both combatants. For example, if someone sneaks up on a sleeping PC and attacks him, you don't roll initiative, you just make the attack. (Some DMs will skip even that and just declare an auto-kill.) You're skipping the full combat rules because they don't apply when both sides aren't in kill mode. In particular, I'm telling you that the ability for a PC to act/react during a combat encounter is a function of his mental state, and that is what the surprise rules seem to be modelling.
Ah, now I understand. We're using the combat round differently. I begin the first round when either side becomes aware of the other, whenever there is the
potential of a fight breaking out. I don't assume that anyone is or needs to be in "kill mode" because the characters or monsters involved may or may not decide to even commence hostilities. Surprise simply gives one side the opportunity to act first, whether it's to attack, close to attack, open a parlay, or run away. Combat itself is hardly ever a forgone conclusion. I usually know what the monsters/NPCs are going to do, but even when that
is to attack, the players could decide that their characters try to avoid the fight, so I'd hardly call that going into "kill mode," but it does happen within the context of a combat round, at least it does in
my games.
"Please point me to the rules that tell me that this is how things work." We're discussing the rationale behind the rules, so the rules you're asking me to point you to are just the ones that started this thread: the surprise rules. If you don't believe the rationale I've conjectured you are free to come up with your own rationale, or to house-rule surprise to work differently.
The rationale I've come up with in reaction to Crawford's response, and a post up-thread, is related to how I use the combat round to reflect the fact that at least one side knows about the other. Surprise is simply the state of becoming a participant in a combat round without knowing about the presence of the other side from the outset. You are surprised when, at the start of the encounter, they know
you are there and you don't know
they are there. That's enough for me and doesn't require any of the participants to have a particular mental state. I let my players decide what their characters are thinking in and out of combat, and whether it's round one or round two.