The way it worked for decades, some obscure player would transfix the world with an unforgettable goal or a few brilliant dribbles at a World Cup or European Championship. Some big club, treating the tournament as a scouting opportunity, would buy him. The signing of a “World Cup star” would delight fans and media. But usually everyone came to regret it.

Take Arsenal’s purchase of Danish midfielder John Jensen in July 1992. The month before, he scored a cracking, long-range goal as Denmark upset Germany in the European Championship final. Arsenal’s then manager, George Graham, told the media that Jensen was a goal-scoring midfielder.

Except he wasn’t. The goal against Germany had been a one-off. Jensen would go years without scoring for Arsenal. His failing eventually turned him into a cult hero: whenever he got the ball, even in his own penalty area, the crowd at Highbury would joyously shout, “Shoot!” By the time Jensen left Arsenal in 1996, he had scored one goal in four years. (Arsenal fans printed T-shirts saying, “I was there when John Jensen scored.”)

Graham had foolishly extrapolated from that one famous goal against Germany. A tournament is a tiny sample of games and moments, but because it feels so important, clubs have tended to read too much into it.

Even Sir Alex Ferguson fell into the trap. He wrote after retiring: “I was always wary of buying players on the back of good tournament performances. I did it at the 1996 European Championship, which prompted me to move for Jordi Cruyff and Karel Poborsky. Both had excellent runs in that tournament but I didn’t receive the kind of value their countries did that summer … sometimes players get themselves motivated and prepared for World Cups and European Championships and after that there can be a levelling off.”

In fact, the worst time to buy a player is immediately after he has done well at a big tournament. All clubs have seen how good he is, so he is probably overpriced, but also exhausted and quite likely sated with success.

And a tournament is a tiny sample of matches on which to base such an expensive decision. If you watched only this World Cup, you would conclude that Colombia’s Juan Cuadrado was better than Lionel Messi. Context also matters. Nacer Chadli shone against Brazil, as part of an excellent Belgian team that he knows intimately. He has rarely looked world-class for Spurs or West Bromwich Albion, though.

Perhaps a World Cup can reveal what a player is capable of. But that fact is not so interesting. What matters is a player’s normal performance, week in and week out. A brief tournament in unrepeatable circumstances does not show that. In 2010, after Asamoah Gyan’s good World Cup with Ghana, Sunderland paid a club record of £13 million for him. A year later, they let him go to the United Arab Emirates.