Traders work on the floor at the New York Stock Exchange, December 9, 2019.Brendan McDermid | ReutersWhat a decade it has been. The year 2010 began with fear that the financial crisis might continue for years. The year 2019 has ended with a 10-year stock market rally.Along the way, one factor has dominated the minds of investors: the search for growth. Technological advances have hastened the trend toward winners and losers and have made growth harder to find. As a result, investors have paid up to get growth — often not GARP, or growth at a reasonable price, but growth at any price.They found it in technology and consumer discretionary, the sectors that had far and away the biggest gains in this decade.Top sectors 2009-2019Technology: Up 328%Consumer discretionary: Up 301%Health care: Up 245%Industrials: Up 193%Consumer staples: Up 140%Bottom Sectors 2009-2019Real estate: Up 130%Utilities: Up 116%Materials: Up 99%Communication services: Up 59%Energy: Down 1%Source: CFRAWhat’s next? Investors should avoid the fallacy that the future will look exactly like the past.It’s often been noted that stocks — and even sectors — that outperform one year often underperform the following year. It’s called mean reversion, the tendency for most investments to revert to long-term averages.This phenomenon also appears to work over very long periods of time — decades.”No one knows for sure, but on a sector level, history implies (but does not guarantee) that the best sectors in the prior decade will not repeat as leaders in the coming decade,” Sam Stovall, chief investment strategist at CFRA, said in a recent note to clients.Stovall noted that in the period from 1990-1999, the top three sectors (technology, health care, financials) underperformed the following decade (2000-2009) on average, while the bottom 3 sectors (utilities, materials, energy) outperformed.Mean reversion?Top three sectors from 1990-1999: Down 28% in 2000-2009Bottom three sectors from 1990-1999: Up 46% in 2000-2009Source: CFRAThe same phenomenon happened in the following decade. In 2000-2009, the top 3 sectors (energy, consumer staples, materials), tended to underperform in the next decade (2010-2019), while the bottom three sectors (communication services, technology, financial) tended to outperform.Mean reversion?Top three sectors from 2000-2009: Up 80% in 2010-2019Bottom three sectors from 2000-2009: Up 184% in 2010-2019Source: CFRABottom line: Investors should be taking a close look at the three laggards this decade: materials, communication services, and particularly energy, which is the only sector that is essentially unchanged over a 10-year period.Why does mean reversion seem to work as an investment strategy? For the stock market, there are several likely explanations. First, in a capitalist system, underperforming sectors tend to be ruthlessly restructured until they are efficient.Another explanation: Humans tend to continue buying things that keep going up in value, creating bubbles that eventually burst.”Crowd-driven momentum pushes trends to extremes,” Stovall said.