Life, as the saying goes, is what happens while we’re making other plans. At this year’s US Open, the plan was clear and longstanding. Everyone—fans, TV commentators, the world-wide tennis community—expected Carlos Alcaraz, the 20-year-old star from Spain, to play Novak Djokovic for the title.

 After winning last year’s US Open, then beating Djokovic at this year’s Wimbledon, Alcaraz started to be hailed as unbeatable. Of course pro tennis has a notoriously short memory. Even most of the tennis press seems to suffer from amnesia. Alcaraz, according to many reports, had achieved unprecedented results for his tender age. This ignored the record of Bjorn Borg, Mats Wilander and Boris Becker, all of whom had won more Grand Slam titles at the age of 20 than Alcaraz has.

 On paper the Alcaraz vs Daniil Medvedev semi-final seemed done and dusted. The Russian, it was assumed, just couldn’t compete with the Spaniard’s power, shot placement and variety of strokes. But fortunately tennis matches are played on court, not on paper, and from the very first set it was obvious that Medvedev, at 6 ft 6  with a wingspan like a condor’s, could keep up with Alcaraz from the back court and serve well enough to pin Alcaraz on the baseline. This forced the Spaniard to take more risks, including frequent forays to the net where all too often Medvedev sent passing shots streaking by for winners.

 After taking the opening set 7/6 in a tiebreaker that wasn’t really close, Medvedev overwhelmed Alcaraz 6/1 in the second set. The Spaniard showed his inexperience, especially in his naïve shot selection. He has an effective drop shot but it became all too predictable and Medvedev frequently swept to the net and put the ball away.

 Alcaraz did rebound and win the third set 6/3, but he frittered away multiple opportunities to seize control of the fourth set. Over and over he had break points on Medvedev’s serve and ads on his own serve but could never convert them for winners.

 Even as Medvedev served at 5/3 for the match, Alcaraz had his chances, but his celebrated consistency deserted him and each of his winning shots quickly alternated with mishits of what looked to be easy points.

  Still, after Alcaraz’s defeat, a betting man would probably put money on his enjoying a long, successful career. Not as long and successful as his countryman Rafa Nadal or as Novak Djokovic who played Medvedev in the US Open final. The Spaniard is young enough to have learned a good lesson from this loss.

 Would that tennis fans and prognosticators learn the same lesson. In tennis as in life, assume nothing. Prove it on court.

  Michael Mewshaw is the author of 23 books including four about professional tennis.