A downturn following the collapse of an asset bubble — an episode of speculative booms in asset prices — can be severe and sustained, with output and employment often lower than in the prebubble economy. This Economic Brief considers some possible theoretical explanations. It argues, based on insights from a simple economic model, that the interaction among financial frictions, wage rigidity, and the constraints of monetary policy near the zero lower bound is a key source of inefficiency in large bubbles. One potential remedy is to regulate speculative investment on bubbly assets so that individual investors internalize their investments' effects on systemic risk.