https://en.wikipedia.org/wiki/Pairs_trade

The most famous pair trade was this: in the morning of a trading day you buy the stocks that performed the worst yesterday and short the ones that performed the best. Because the market reverts to the mean, this strategy made money hand over fist from the 1980s when Morgan Stanley started using it until the summer of 2007 when somebody fat fingered a button, unwinded their position during the day, and crashed everybody else who was in this trade.

The profitability of that trade went downhill long before that crash but since then it's been impossible to make money doing it. (When there's a hedge fund bubble the profitability of a trade drops gradually as more people pile into it and the market inefficiency it targets is dispelled, quite different from an equity bubble which goes up dramatically until...)