Context: Aang (“A”) is a classic Batman’s Rule (never kill) hero, as a result of his upbringing in Air Nomad culture. It appears to him that he must kill someone in order to save the world. He is the only one who can do it, because he’s currently the one and only avatar. Yangchen (“Y”) is the last avatar to have also been an Air Nomad, and has probably faced similar dilemmas in the past. Aang can communicate with her spirit, but she’s dead and can’t do things directly anymore.
The story would have been better if Aang had listened to her advice, in my opinion.
Overthinking issues that are really very simple
Counter-signallign as a smart-person mistake
Valuing intelligence above all other qualities
Rigidly adhering to rules—compare the two endings of “Three Worlds Collide” and the decision by which they diverge.
Expecting other people to always be rational
Got nothing for the last two. I don’t think the last one is a mistake that very many people at all make. (I think being right about things has surprising benefits well past the point that most people can see it having benefits).
Other smart person mistake covering posts that spring to mind: http://lesswrong.com/lw/dxr/epiphany_addiction/ http://lesswrong.com/lw/j8/the_crackpot_offer/
And a lot of the general mistakes that LessWrong warns against are just person mistakes, rather than smart person or normal person mistakes. [edit: grammar]