All this talk about Sans breaking his promise and all that. No no, I have an idea. He seemed to genuinely think he did a good job at protecting you when he was talking about it at the MTT Resort.
(If you haven't died up to this point)
And the fact that he literally had to ask himself if he was wrong about him doing a good job at protecting you if you died makes me think that this belief that he did well was genuine.
So I was just thinking that maybe there was some behind the scenes stuff going on when it came to Sans' protection. Like, can you imagine Sans successfully managing to stop a threat from getting to you, only for another threat to come and kill you while Sans is giving himself a pat on the back?
Sans: (after successfully stopping someone from attacking Frisk) aw, heck yeah. i'm doing such a good job at this promise thing. that deserves a celebratory hot dog.
Frisk: (f*cking dies behind his back)
Sans: (oblivious) i'm the best.
Listen, Sans is very smart and observant, but even he tends to miss some crucial details. Like his special attack? He failed to consider that maybe using up all his energy to fight and THEN doing the special attack wasn't really the best idea? Or even just fighting in the first place? I wouldn't put it past him if he missed out some potential threats when trying to protect you/Frisk. Either that or he prefers to let you fight your own battles. Or both. It could definitely be both.
You know, I'm just gonna go out in a limb here and say that Sans deserves the title of being the smartest dumbass in the game. He's a very very clever idiot. Good job, Sans.