Grant opens by arguing that while people spend significant effort updating their skills, wardrobes, and technology, they rarely apply the same updating mindset to their own opinions and beliefs — treating rethinking as a distinct, underdeveloped cognitive skill worth deliberately cultivating.

Core argument he establishes:

• Grant identifies several thinking "modes" people default into — preacher (defending sacred beliefs), prosecutor (attacking others' views), and politician (seeking approval) — none of which prioritize genuinely updating one's own views based on new evidence
• He advocates instead for a "scientist" mindset — treating one's own opinions as hypotheses to be tested and potentially revised, rather than positions to be defended
• This reframing sets up the book's broader argument: intelligence is often measured by the ability to think and defend an argument, but wisdom requires the added ability to rethink and update that argument when warranted

This opening framework distinguishes different cognitive stances toward one's own beliefs, setting up rethinking as a deliberately cultivable alternative to the more common, defensive modes.