Main takeaway from the book is emotions are as important as fact in persuasions, especially when the audiences have established ideas.
The book starts with conspiracy theories and charismatic leaders. In both scenarios, ideas are planted into audience's minds and reinforced with emotions. The association of ideas and emotions means that when the emotions are aroused, the ideas surface as well, even if the ideas are incorrect. In later chapters, the authors also explain that System 1 thinking, which is fast and energy efficient, is primitive but very effective learning method. Thus, it is impossible to complete eliminate emotions from memorizing.
One thought mentioned in the book, but worth more exploration, is polarization in groups. Why joining groups tends to polarize group members' ideas? The book briefly mentioned that empathetic emotions appeal to group members and reinforces ideas. But why polarization tends to happen?