The negativity bias favours the cultural diffusion of negative beliefs, yet many common (mis)beliefs-naturopathy works, there's a heaven-are positive. Why? People might share 'happy thoughts'-beliefs that might make others happy-to display their kindness. Five experiments conducted among Japanese and English-speaking participants (N = 2412) show that: (i) people higher on communion are more likely to believe and share happier beliefs, by contrast with people higher in competence and dominance; (ii) when they want to appear nice and kind, rather than competent and dominant, people avoid sharing sad beliefs, and instead prefer sharing happy beliefs; (iii) sharing happier beliefs instead of sad beliefs leads to being perceived as nicer and kinder; and (iv) sharing happy beliefs instead of sad beliefs fleads to being perceived as less dominant. Happy beliefs could spread, despite a general negativity bias, because they allow their senders to signal kindness.