Fed chairman Ben Bernanke can't understand why, after pumping trillions of dollars into the economy, the US is still mired in a no growth, slow growth period.

ABC News:

"We don't have a precise read on why this slower pace of growth is persisting," Bernanke said. He said the weak housing market and problems in the banking system might be "more persistent than we thought."

It was the Fed chief's most explicit warning yet that the economy will face serious challenges next year. For several months, he had said the factors working against economic growth appeared to be "transitory."

The Fed cut its forecast for economic growth this year to a range of 2.7 percent to 2.9 percent from an April forecast of 3.1 percent to 3.3 percent. It also cut its forecast for next year to a range of 3.3 percent to 3.7 percent from an earlier 3.5 percent to 4.2 percent. The Fed also said unemployment would stay higher than it had expected earlier.

In a policy statement issued at the end of a two-day meeting, the Fed blamed the worsening economic outlook in part on higher energy prices and the earthquake and tsunami in Japan, which slowed production of cars and other products.

But at a press conference afterward, the second of what the Fed says will be regular question-and-answer sessions with reporters, Bernanke conceded the economy's troubles are more puzzling and potentially more long-lasting than a pair of temporary shocks.

Wall Street hardly reacted at all to Bernanke's candid admission of cluelessness. They know what they've got when dealing with the Fed chairman and the fact that the economy is a mystery to him causes no one to bat an eye.