Why do so many economists fear a 1929-style crash?

Core Viewpoint - The stock market's three-year bull run indicates a general optimism among Americans, despite contradictory poll results suggesting a more pessimistic outlook [1] Group 1 - The stock market has experienced a three-year bull run, reflecting positive sentiment among investors [1] - Polls indicate a discrepancy between public sentiment and market performance, with many Americans feeling less optimistic [1]