1) A breakup of the euro zone.
2) A U.S. slowdown.
3) A hard landing in China .
4) Geopolitical risks (such as Iran).
Central bank actions and the wall of liquidity chasing assets may have helped insulate the financial markets from the state of the “real economy,” Roubini says, but that situation cannot last forever.
It looks to me like Roubini basically is the source of the wall of worry that the market must climb!