Abstract Earlier research finds correlation between sentiment and future economic growth, but disagrees on the channel that explains this result. We shed new light on this issue by exploiting cross-sectional variation in country size and market efficiency. We find that sentiment shocks in the largest advanced economies increase economic activity, but only temporarily and without affecting productivity. Conversely, sentiment shocks in smaller or less advanced economies predict prolonged economic growth and a corresponding increase in productivity. The results support the view that sentiment can create economic booms, although only in economies where sentiment and fundamentals are harder to disentangle.