John Bogle had a nice interview that I had found on Youtube. I'm too lazy to find the exact interview but I'll paraphrase what he said.
He said that in all his years in the industry, he has not met anyone who successfully timed the market (by which he means timing bear vs bull cycles). He said that he did get a bad feeling during the dot com bubble and reduced his equity allocation slightly, but that was the only time he successfully "timed" the market. He then admitted that earlier in his career, he had tried timing around bear markets -- but failed to guess correctly.
