Lockhart, Dennis

[It is a] very difficult policy to intervene in the workings of markets at a particular chosen time.

It's difficult to identify, it's difficult to choose timing, difficult to be sure that market forces themselves will not have what
turns out at the end to be a positive effect.

From audience Q&A, as reported by Market News International, saying he's not "comfortable" with the Fed pre-emptively targeting asset bubbles.