AI never surrendering no matter how outmatched or dead they know they are, ever!
This is a hilarious thing in DF adventure mode. If I wrestle someone to the ground and cut one of their appendages off, then demand they hand me a pouch of coins, they refuse! How dumb do you have to be. Fortunately, I can just wrestle it away, knock them out and gain possession, or kill them and pick it up, but you'd think they'd value self preservation.
I've also noticed this quite a bit in strategy games, like Civilization 5. Even if I'm twice as large as an enemy civ and have the military power to crush them lined up at the border, they refuse if I demand just a few gold per turn or some of their luxury resources. It's kind of stupid, really.
I've noticed the same to a lesser extent in Crusader Kings II, where you need a 100% war score in order to get AI to surrender. Sometimes this makes sense in a holy war, county conquest, or de jure war in which they will lose everything by surrendering, by when surrendering ends with them being vassalized and it's they're 1,500 troops against my 15,000, and I'm at 50% score, they stubbornly won't surrender(although we can have white peace). Sometimes content characters will offer surrender at 80%, or I can press my claims at 97%, but it stills seems odd when they stick it out for so long. The reason I find this odd, is that, theoretically, if you were about to be forced to swear fealty to someone, surrendering early and accepting it would increase their opinion of you because of your compliance. It can be even better when they are gaining the protection of a very powerful liege, so their resistance doesn't make sense in some cases. Fortunately, this game is generally pretty logical about this, making it possible to vassalize much smaller realms peacefully if you shares religion, share a border, and are much stronger, but oddities appear.