It's very interesting that Kaladin is refraining from jumping into the defense of the tower and being the hero like he normally would. He doesn't have the mental well being to do it. It feels in general like we might be moving towards an end for him where he *truly* is done with fighting, and his new purpose helping the mentally ill is his calling. He's done with the battle. In a vacuum, I think that's a phenomenal character path for Kaladin and love the idea of going down this road with a character like this. In the context of the Stormlight Archive and the events happening, though, I think that would be pretty deeply unsatisfying for our #1 guy to just... stop contributing to the major war effort. I don't think that's what will end up happening.
What I've been thinking will happen is that discovering that some of the mentally ill just cannot be helped and truly DO need to be isolated and kept away from all others for everyone's safety and for their own protection, or that some people that you bring out of the sanitarium WILL end up killing themselves despite best efforts, will be what triggers Kaladin to accept the Fourth Ideal and say the words. I don't think it's ever been revealed in the text, and I've avoided hearing any Word of Brandon or online speculation on the matter, but I've suspected the Fourth Ideal is something along the lines of "you can't save everybody. you have to let some people die and/or suffer." Kaladin's hero complex has always forced him to put the burden of saving everyone onto himself. He's never been able to detach himself enough from the people he's sworn to help enough to accept that he can't help them all like Lirin is able to. Throwing himself into this mental illness crisis is a great way to confront that issue away from the battlefield.
It's also been mentioned (i forget if by the Sibling or Raboniel) that a Radiant of a high Ideal might still be able to use their powers inside the tower. So if he swears the Fourth Ideal, he could possibly have a decisive impact on this invasion.
The problem here though is that the mental illness treatment arc hasn't progressed far enough before this invasion for Kaladin to get to that point. So I'm not sure this is really possible. It sure seems like Navani won't be able to retake the pillar without him, even if she has her own crowning moment of awesome and becomes a Bondsmith with the Sibling. Maybe the invasion will be successful after all?
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The batman villians all seem to be one big joke that batman refuses to laugh at - SantaRPG