When Rory Lamont first burst on to the rugby scene at the start of the Noughties, there were plenty of predictions that the twinkle-toed back would become one of the all-time greats for his country.

He was blessed with rapid pace, an eye for an opening and a mesmerising sidestep, and when he ghosted past opponents into the international ranks, following his Test debut against Wales in 2005, it seemed the SRU had unearthed another diamond. But ever since, on his injury-strewn peripatetic path, when it has come to accruing caps, Lamont has grown ever dozier.

What a contrast between the Glasgow Warriors man and his compatriot, Allan Jacobsen, both of whom have slipped into retirement from the professional game this week. Whereas Lamont was one of life's cerebral fellows, who took his sport pretty seriously and queried the meaning of existentialism, "Chunk" thrived at the coalface, either providing yeoman service in the scrum for Edinburgh and Scotland, or toiling away at establishing a plumbing business, while maintaining his relationship with the Preston Lodge personnel, whence he emerged as a teenager.

Lamont, a glittering presence in the early stages of his career at Glasgow, soon developed itchy feet and moved to Sale Sharks, then Toulon, but despite being widely regarded as a more gifted individual than his brother, Sean, the sparkling vignettes and lustrous feats gradually drifted out of his repertoire as he sustained one knock after another. Jacobsen, by contrast, was capable of transcending any adversity and eventually accumulated 65 caps – more than twice Rory's haul of 29 – but he did so from within the bowels of Murrayfield, never inclined to leave Edinburgh.

There are two or three lessons to be absorbed from the divergent paths taken by these disparate characters. Firstly, their stories emphasise how often luck plays a part in whether anybody is perceived to be a success or failure. As a teenager, Jacobsen nearly suffered grievous damage after being involved in a car crash. "A piece of glass cut me half an inch from my jugular vein," he said this week. "Maybe it was something that shaped me into deciding to make the most of my life after that."

Lamont, in his salad days, enjoyed the sort of serene progress which might have indicated he was destined to be lucky, on and off the pitch. Yet, the longer he was involved with the game, the more his fortunes ebbed and flowed and the meagre tally of six appearances he has made since returning to the Warriors in 2011 explained why there was a sombre tone to his valedictory comments.

"I have been struggling with injury for some time now and it is clear that I won't be able to get back to the level I was playing at before," he lamented. "But it has been a privilege to see the boys do so well."

Jacobsen, on the other hand, has bowed out on his own terms and earned widespread praise for his phlegmatic approach to dealing with Kipling's twin impostors. At 34, he has risen above the often miserable results endured by Edinburgh and ploughed on remorselessly, gaining kudos and offering clout even as the scrum collapsed around him. Recently, Lamont had become peripheral and he gained more coverage for calling Barack Obama a "Wall Street whore" on Twitter than bewitching and bewildering his rivals.

As inter-city contemporaries, they were opposites, but neither conformed to the stereotype of their city. "Chunk" was all grisly muscle and down-to-earth banter and one suspects he will be happier dealing with burst pipes than getting dressed up in black tie for glitzy sports functions; Lamont, by comparison, rarely looked in his comfort zone when asked to get down and dirty. Instead, it was Sean who proved to be the more influential.

Rugby, of course, has always been a pastime for every shape and size and men and women from every conceivable background. How else do you explain the triumphs of the diminutive, but tough-as-teak Jacobsen, who has not ruled out the possibility of returning to his roots at Preston Lodge, and the travails of the mercurial Lamont, whose joie de vivre has gradually evaporated, amid his frequent spells in hospital wards?

Gregor Townsend, the Glasgow coach, struck the right balance, when he said: "We were all hoping [Lamont] would make a full recovery and show what he could do in a Warriors jersey." The word "but" hung in the air, as it often does in these circumstances. Yet there are some adversaries who nobody can beat.

As for Jacobsen, he now has his own Twitter account, and a trophy moulded in his own inimitable shape. Precious few people would have forecast that was how their lives would have panned out at the beginning of their careers.