Andy Murray is going to be a father in February according to best estimates – which might inconvenience his participation in the Australian Open in January – and everybody is happy for Britain’s best player and his wife, Kim.

However, the rush this week to celebrate their impending parenthood by linking it unequivocally to Murray’s excellent form (since they married in April, he is 27-4, including a strategic walkover in Rome and a blip loss in Washington this week) is fuelled as much by sentiment as science.

It is an understandable urge. Everyone wants to see Mr Grumpy smiling and winning, but Mr Grumpy has shown us down the years he is capable of winning or losing whether he is grinning idiotically or swearing his head off.

This is a conundrum Murray has wrestled with for a long time and his revelation recently that he has been talking to a psychiatrist to better understand the workings of not just his own mind shows his concern.

There is no sensible reason to assume Murray is more or less likely to win a third grand slam title at the US Open next month because he is contemplating the joy of sleepless nights than there is to say that Roger Federer, proud father of two sets of twins, will continue to be the game’s éminence grise until his right arm drops off or he collapses in a 34-year-old heap at Flushing Meadows.

After all, the daddy of all tennis daddies has won four of his 17 majors since he married Mirka Vavrinec in April 2009, followed quickly by the arrival of their first twins: the Rafael Nadal-free French Open and Wimbledon that year, the Australian Open final in 2010 against Murray and the 2012 Wimbledon final, also against Murray.

Those are numbers that hardly diminish Federer’s achievements, but they lend them perspective. Was Federer a better player before he became a father? Perhaps, although it is difficult to say – but certainly he was younger.

What of the seemingly eternal Spanish bachelor Nadal? Will he or won’t he, at 29, add to his 14 slam titles if there is any substance to the rumour that he has finally asked Xisca Perello to marry him?

Tomas Berdych announced his engagement to Ester Satorova at the Australian Open this year (didn’t loyal Kim give him her tuppence worth during Andy’s win over the Czech in the semi-finals?) and they married last month. It will be interesting to see how he finishes the season.

While it is clear Murray at 28 is playing with a smile on his face and has rediscovered the freedom of his youth, there is a better case to be made that this stems from a hard-headed decision to fine-tune his tennis, a strategic shift encouraged, as it happens, by Amélie Mauresmo, who is due to give birth any day.

If anything, Murray is a more aggressive ball-striker since Mauresmo’s arrival in his life in 2014 than he was in the two years he played under the guidance of the stridently macho Ivan Lendl. So there, at least, is some evidence that he responds as much to understated encouragement as he does to loud, male hailing.

The view that the only happy athlete is a married athlete is a societal judgment, not unlike the one this government would like to impose on unmarried parents or partners of inconvenient gender. As Murray said after losing to Djokovic in the Australian Open final this year, success is being happy. What he did not say is that happiness is being successful.

Take, for instance, Stan Wawrinka, who won his second major by winning the French Open this summer despite the weight of a publicly crumbling relationship with his wife and the apparent marital serenity of the man he beat, the ever-smiling Djokovic. He rose above his circumstances because, correctly or not, tennis defines him.

What is apparent from sporting history is special athletes are capable of compartmentalising their lives. They have the selfish gene, the one that blocks out all others. Muhammad Ali had some of his greatest wins while his personal life was in turmoil, as did Mike Tyson for a long time.

Still, it is stating the obvious to point out we are all different, even champions. Caroline Wozniacki said a couple of months ago of her split with Murray’s close golfing friend, Rory McIlroy, at the start of 2014, “I didn’t know how strong I was until that happened.”

Wozniacki struggled for more than a year then prospered again, pretty much to the limit of her abilities. McIlroy, meanwhile, established himself as the best in the world, Jordan Speith notwithstanding.

In sport, myth too often conquers fact, or at least wrestles with it. Don’t believe what you feel; believe what you see. And, even then, have another look. Otherwise the bookies will take you to the cleaners.