Following his team’s loss to Turkey in the final game of their group stage, the US soccer team’s manager Mauricio Pochettino complained about the use of the word ‘momentum’ in sports.

“[Momentum] is a topic that I don’t understand,” Pochettino said when asked about how the loss would affect his team’s prospects. “What is momentum? To play with the same team that we played against Australia? And to take the risk to receive a yellow card and not to play the next game? Did Germany lose the momentum too [in their 2-1 loss to Ecuador]? I don’t know. [There are] too many topics in soccer that I don’t understand. The objective was to finish first, and we are first, and now is the next stage, and it’s going to be a final, and we are ready.”

Pochettino has a point. There is no doubt that a team is happy when they win and sad or disappointed when they lose. But ‘momentum’ is one of those words that have a scientific sheen and used to give weight to the idea that there are ‘hot streaks’ and ‘cold streaks’ in sports, that a win will likely increase the chances of a win next time and a loss will lead to more losses. But one result is not a trend, though the word ‘momentum’ seems to suggest that it can be.

But the broader question is whether there such things as streaks at all. One can point to streaks after the fact but are they predictive of the future? For a long time, it was thought that this was an illusion held by players and fans alike, and led to the idea that people are irrational, having beliefs and making decisions that lack statistical support. The illusion hypothesis found support in a study of basketball.

Thomas Gilovich, a graduate student in the early 1980s, began comparing the widespread perception of hot streaks in basketball to the hard data. Gilovich, now at Cornell, led a study showing that the hot hand didn’t really exist: The shooting records of the Philadelphia 76ers provided no predictive value of subsequent shots. A player might be hot one minute, but not the next. Fans and even sports professionals, they concluded, were making decisions based on myopic impressions.

But others said that that analysis was flawed. Another study by Jeffrey Zwiebel and Brett Green says that basketball may not be the best sport to study this question, and that baseball may be better.

Zwiebel and Green argue that the original finding failed to account for a key issue. In basketball, the opposing team quickly adjusts to a “hot” player, devoting extra coverage and forcing that player to attempt more difficult shots. As a result, it’s inevitable that a hot player’s shooting percentage will decline. It’s not because the hot streak was an illusion, but rather that the hot player attracted more opposition.

Baseball is different, because pitchers and coaches have very limited ability to re-deploy resources against a hitter on a hot streak. Pitchers and coaches do play to a hitter’s particular weaknesses, but they can’t put more people in the hitter’s way.

A more sophisticated analysis of basketball statistics found that streaks existed even in that sport.

As it happens, a team of Harvard researchers reached a similar conclusion in a new study of basketball. The Harvard team looked at data on 83,000 shots made during the National Basketball Association’s 2012-2013 season. But instead of looking simply at completion rates, the researchers built a model for gauging the difficulty of shots. They found that players who had exceeded their expectations in recent shots were likely to face tighter opposition and take more difficult shots. Adjusting for the increased difficulty of the shots, the researchers found that hot players were likely to continue outperforming. The “hot-hand effect,” they estimated, raised their chances of making a shot by 1.2% to 2.4%.

Interestingly, the people who study these questions tend to be in business schools because they are very interested in how beliefs drive actions in the marketplace, because those influence what remedies are taken, such as after the financial crisis of 2008 triggered by sub-prime mortgages.

Investment bankers have been criticized for underestimating the risks of subprime mortgages, for being irrational in their optimism. But it’s possible that their excessive risk-taking wasn’t irrational as much as it was encouraged or even subsidized by regulatory policies, such as those that protected banks considered “too big to fail.” The difference between those two diagnoses of the financial crisis leads to very different proposals for reform.

“One can portray the financial crisis as being triggered by a bunch of mistakes, or one can portray it as the consequence of risky decisions that were made based on the incentives and subsidies in the system,” he says. “I see it as more of the latter.”

People tend to extrapolate into the future from current events. This is especially true in politics and the stock market where pundits make a living by reading the tea leaves and predicting what will happen next. In politics right now, progressives seem to be on a bit of a roll in the Democratic party while the Trumpers are on a streak in the Republican Party. But all it would take is for one or two reversals for the pundits to all claim that the opposite in the trend.