The Assuredness Movement is spoken of by Jasnah to Shallan when Shallan is discussing her research of the Alethi monarchy with Jasnah. This stems from Shallan's study of the history of the monarchy, at Jasnah's insistence as her patron. Shallan's opinion of the scholars included in the volumes defines their case as one of arrogance, or "errorgance", since they refuse to see any other point of view on the subject of the monarchy but their own.
Jasnah describes that "errorgance" is a literary device and that the scholars are intentionally overstating their case; that this is The Movement, that they are trying to provoke discussion. Shallan decides that she could get behind it, because she feels she could much better stab it in the back from that position.