Rosa Parks was a seamstress and activist who famously helped launch the Montgomery bus boycott and the civil rights movement when she refused to give up her seat on a segregated bus in 1955. Duhigg argues that the boycott was successful because Parks had a wide range of friends and acquaintances across Montgomery’s Black community. He uses Parks’s protest as an example of how social habits—like defending friends and succumbing to peer pressure—can spur social change.