Joe Stiglitz, The Politics of Economic Stupidity:

[L]ow interest rates will not motivate firms to invest if there is no demand for their products. Nor will low rates inspire individuals to borrow to consume if they are anxious about their future (which they should be)…. Demand is what the world needs most. The private sector – even with the generous support of monetary authorities – will not supply it. But fiscal policy can. We have an ample choice of public investments that would yield high returns – far higher than the real cost of capital – and that would strengthen the balance sheets of the countries undertaking them.

The big problem facing the world in 2015 is not economic. We know how to escape our current malaise. The problem is our stupid politics.