QE isn't printing money, it is a way to blend treasuries into a finely chopped liquid so that your bank can keep the asset side of its balance sheet just as liquid as it's deposits. Due to liquidity preferences people prefer liquid assets over illiquid assets and therefore demand compensation to give up liquidity. Since the yield on capital is falling, people prefer holding straight up money over investing it themselves in risk bearing assets, this means banks are being flooded with short term demand deposits that can be pulled out at any time. What QE does is effectively make all banks hold treasuries collectively. If one bank sends $1000 to another bank it doesn't have to sell treasuries at the current market rate and instead they just transfer the bank reserves which are a claim on $1000 worth of treasuries. As demand deposits become a greater share of financial capital, the risk of a bank run on a specific bank becomes higher and higher. Basically any bank is at risk of becoming instantly insolvent. The problem here is keeping excessive savings in money instead of capital.