Good source of “book ideas” — Assumptions that people hold
e.g. “Ego is the Enemy” is going to be a powerful book for anyone that believes that ego is useful
“Why you shouldn’t start a company” is going to be powerful for people that believe they should start a company (perhaps they’ll just look for why it doesn’t apply to them, but still)
“Why the purpose of life isn’t satisfaction” will be intriguing for anyone that holds that opinion
And so on.
Opinions that people hold close and believe emotionally but wouldn’t necessarily be able to articulate a coherent logical argument for why they are true.