You'd have to do your research. When everything's gone to hell and people are cursing the markets is probably a good time, though. But when others are selling, as Buffett and probably a good number of other investors say.

I think Buffet said something to the effect of "be fearful when others are greedy, but be greedy when others are fearful".

Having lots of dry powder in a downturn is a very good place to be for a professional investor. That said, most folks are not professional investors, so buy and hold is relatively simple strategy that performs fairly well for non-professionals.

people with suits looking even more depressed than usual