Maybe he meant the toolbox of some economists...

Greg Mankiw has a piece up at the New York Times that opens with this assertion: "Nothing in the toolbox of economists makes us good stock pickers." The article does a good job explaining the relevant economics concepts to a lay audience (as expected given the author), but I did notice a slight but amusing omission from this:

Advocates of market rationality now say that stock prices move in response to changing risk premiums, though they can’t explain why risk premiums move as they do. Others suggest that the market moves in response to irrational waves of optimism and pessimism, what John Maynard Keynes called the “animal spirits” of investors. Either approach is really just an admission of economists’ ignorance about what moves the market.

I'm not entirely sure Keynes would have conceded that point:

Keynes was ultimately a successful investor, building up a private fortune. His assets were nearly wiped out following the Wall Street Crash of 1929, which he did not foresee, but he soon recouped. At Keynes's death, in 1946, his worth stood just short of £500,000 – equivalent to about £11 million ($16.5 million) in 2009. The sum had been amassed despite lavish support for various causes and his personal ethic which made him reluctant to sell on a falling market when if too many did it could deepen a slump.[135]

Just imagine how much Keynes would have socked away if he didn't have that live-for-today attitude.