To quote:

"Buy when there's blood in the streets, even if the blood is your own."

This is contrarian investing at its heart - the strongly-held belief that the worse things seem in the market, the better the opportunities are for profit.
...as Warren Buffett warned, "You pay a very high price in the stock market for a cheery consensus." In other words, if everyone agrees with your investment decision, then it's probably not a good one.