IT began with a cramp in his left hand. The other fingers still raced across the neck of the violin, reliably picking out the notes, but his fourth digit seemed to have taken on a life of its own. The effect wasn’t quite Dr Strangelove – but take up his instrument, and the pinkie suddenly began answering to other gods, flexing and contracting on its own terms. The condition was strangely task-specific. In any other context, the rebellious fingertips responded as telt. But pluck up the violin, and the fourth finger got stuck to the string.

Being an adaptable animal, he compensated. If Shostakovich or Wagner demanded the note, he played the note, devising weird workarounds to help out his sleepy fourth finger. And he did all of this alone, in full auditoriums, in front of a full orchestra. It is difficult to imagine the mental energy – the stress – that went into keeping the show on the road. But when the cramp slowly crept through his third finger, he knew in his bones he couldn’t keep jury rigging his way through Beethoven and Brahms. It was over.

Doctors call the condition focal dystonia. It is still early days in neurology, but they reckon it may be down to misfiring neurons bewildering the muscles of the hand, causing involuntary contractions. The condition has affected a clutch of professional musicians, forcing them to relearn their instruments with the unaffected hand, or silencing them altogether. Sadly for my friend’s friend, his stellar career as a violinist was cut short. The cruel irony of his story always stuck with me. It seems like a particularly poetic kind of injustice.

Precisely because of his mastery of the instrument, precisely because of the hours of toil he put into making it sing, he was deprived not only of his vocation, but also his most eloquent mode of self-expression. Every life has its challenges and its disappointments, but the existential cruelty of what happened to him seems particularly acute.

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Nobody destroys their capacity for accountancy by being a really good accountant. Mastering the detail of statutes doesn’t atrophy your lawyering skills. Writers may experience the occasional cramps – but you can always dictate.

The dystonia didn’t just deprive him of an activity he loved – it also threw his identity into jeopardy. Some people might say “I play music for a living”, but that’s a mile away from approaching the world as a musician. I write, but I’m not a journalist. I teach, but I’m not a teacher. What do we call a musician who can’t play a musical instrument? Who is a virtuoso who can no longer carry a tune?

Watching Andy Murray’s tearful press conference announcing the end of his professional tennis career reminded me of my musician friend’s troubles. With characteristic candour, Murray told reporters: “I can still play to a level – not a level I’m happy playing at. But also, it’s not just that. The pain is too much really. I don’t want to continue playing that way. I tried pretty much everything that I could to get it right – that hasn’t worked,” the 31-year-old said.

You couldn’t help but be struck by the raw emotion in Murray’s shaking voice, but I suspect it is difficult for us unfit civilians really to understand the psychological weight of this week’s public admission that Murray’s tennis career is entering its final phase.

IN Corpus Christi College in Cambridge, there is a portrait of the 16th-century playwright Christopher Marlowe, who lived fast and died young. In the top-left corner, a Latin maxim reads: “Quod me nutrit, me destruit”. What sustains me also destroys me. The Elizabethans often symbolised this sentiment with an upturned torch, its flame burning brightly, but consuming its own substance. It is an image of passionate, obsessive love.

It’s this touch of the obsessive which, I think, has always made me mildly suspicious of professional athletes. I’ve always valued a bit more of a magpie sensibility, which is a polite way of saying I’m undisciplined and shallow. But there is no room for the dilettante in the world of professional sport or music. You’re rewarded for a single-minded, one-track focus. Devotion. Mental fortitude. Repetition and, I sometimes suspect, a certain lack of imagination.

Like the soloist who must carry the melody, or like the darts professional lining up a triple 20, the business of singles tennis is brutally physically and psychologically exposing. If you don’t return the ball, it will go unreturned. If you can’t reach the lob, you lose the set and the match. If your head isn’t in it, those double faults can multiply.

That’s part of the pleasure of watching the set-to, as bodies and nerves fray as the ball ricochets across the court. But in following the career of an athlete like Murray, there’s also the voyeuristic dimension of watching a young man taking the noblest instrument he has – his lightning nerves, co-ordination, speed, stamina and stretch – and testing them to physical destruction before the eyes of the whole world. It’s a breathtaking arc.

The National:

Andrew Murray poses with the trophy after winning the Under 14s event during the National Junior Championships at the Nottingham tennis centre on August 20, 1999

That’s why there’s a particular pathos to Murray’s honest discussion of the pain he is in. The injured athlete is a banal figure in sports reporting. Perhaps we don’t appreciate the damage folk do to themselves in the bid to render their bodies capable of their fullest physical expression.

“There’s little things, you know, day-to-day, that are also a struggle,” Murray said. “It would be nice to be able to do them without any pain. Putting shoes on, socks on, things like that. I’ve spoken not loads but a number of times to psychologists and stuff about it. But nothing helps because you’re in lots of, lots of pain. You can’t do what it is that you want to do, you love doing. I can do it, but it’s just not fun, not enjoyable doing it any more.”

Murray is a year younger than me. He’s infinitesimally fitter, faster and stronger. You and I can waddle up the high street with a proud and happy gait. Most of us will be able to pull off our socks without agony raking our bones. But this exceptional specimen of human vitality flinches. What sustains me also destroys me.

It is an image of tremendous pathos. It is also an image few sportsmen would have shared. The clichéd macho man of the sports field shrugs off his injuries. He represses his physical complaints. He celebrates and loses – stoically. Murray does it differently. From his earliest days in the public eye, he’s always been an interesting combination of the viscerally felt and douce restraint. It’s a combination, I think, which chimes with many Scots. They will wish him well as he contemplates how to reframe the only life he’s known. Materially, Murray is free in the way few people in our society are free.

We may prefer to remember the triumphs rather than the disasters, recall the victories, not the defeats. But failures are often more interesting than successes. The world breaks everyone. Afterward, many are strong at the broken places. For Andy Murray – for all of us – it is a painful but ultimately valuable.