Consider the U.S. stock market this past month. Look at returns in semiconductor stocks (SMH) over that period; then look at returns in consumer staples shares (XLP) over the same period; and then look at regional banking shares (KRE). Participants in those markets were fishing in very different ponds.
A major source of movement in the stock market comes from rotation from one group of sectors to others, as institutions pursue investment themes. Catching these rotations is a great way to find the best fishing ponds. It's important to make sure we're playing the right games before we work on improving the game we're playing.