Like a cascading hourglass, Brian O'Driscoll's wondrous career, as it must, is nearing its end.
He remains irreplaceable, as last weekend in Northampton once more demonstrated.
You sensed a note of lament in Ian Madigan's voice this week as he pondered the dwindling amount of time he will spend honing his craft alongside one of the game's giants.
"Playing with Brian outside you makes things very easy for you," says Madigan. "One of the strongest parts of his game, which the public wouldn't see as much, is his communication with you during games. He makes it very clear exactly what he wants from you.
"That could be in defence, your positioning, to be a bit wider, or in attack, he'd be very specific in terms of what pass he wants and he works the game off that.
"Last weekend in England it was just to go out and execute upon his command. That's one of the big roles I have now in this team, just to be the facilitator for the players around me."
Those seeking to effect the impossible -- to somehow walk in O'Driscoll's footprints -- are in no doubt as to the impact that their predecessor has made on those around him.
"Yeah," agrees Leinster out-half Madigan. "With Brian, he's not right every time, but he's right 99pc of the time and if you follow his direction you're going to come up with the right decision the majority of the time.
"It is a game of percentages and when he says 'jump' I ask 'how high?'"
Ulster's Jared Payne is Kiwi-born but is already elbowing his way to the front of the queue in terms of putative replacements once he earns residency qualification for Ireland in a year's time.
Initially, after suffering the grievous blow of almost a year-long absence when crocking his Achilles, it seemed as if it might be Rob Kearney's full-back role that was under threat.
Now he is being touted as the solution at No 13 -- although indigenous interested parties such as Luke Fitzgerald, Robbie Henshaw and Keith Earls may have an argument there. Payne's Ulster team-mate Darren Cave, too, has been refreshingly honest in terms of his desire to propel himself into Ireland coach Joe Schmidt's thinking.
However, when Payne is unfettered by injury -- his gliding style is currently hampered by groin trouble -- his eye for the gap and persistence in pursuing the off-load mark him out as a special contender.
However, the 28-year-old former Waikato, Crusaders and Blues player is more concerned with the short-term.
"I'd just like to get out there running freely and get over this groin thing and play the rugby I know I'm capable of," he says ahead of this weekend's Heineken Cup return clash with Treviso in Italy. "It's been a bit frustrating for me lately."
He has heard all the prognostications that have cast him as O'Driscoll's anointed successor. For Payne, it clearly remains a significant long-term goal but realism dictates his perspective.
"I've heard all sort of things recently, even that I'm being loaned out to Leinster all that kind of stuff!" he smiles.
"It's fun to hear things like that. You see all these different stories.
"If you think about it there's a spot there open ready to be taken. Someone has to grab that jersey. If I was playing well enough at the time and got picked it would be an awesome honour.
"There would be pretty big shoes to fill. There will never be another Brian O'Driscoll. He has been a great servant to Ireland and one of the best players the world has ever seen. It would just be a massive honour for me to be anywhere near that team."
The horrific injury that marred his debut season with Ulster happened on duty against Treviso so one can sense his reluctance to cast his eye further than this weekend's clash.
Added to that, of course, is the fact that Cave's superb form ensures that, bar a brief sortie earlier this campaign, the smooth-running Tauranga man is likely to remain at full-back this weekend.
"You can have a bit more influence on the game at 13," he admits.
"We're a good team and when everyone is fit and firing, we know what we can do. Once we get Tommy Bowe back in the groove, it will be interesting to see what the team will be capable of producing.
"I just have to play as well as I can wherever I'm put and then get selected wherever the coach puts me.
"The groin is still an ongoing issue. I hurt it in the opening couple of minutes last weekend and to have to look after it. Sometimes you have to toughen it up, grin and bear it and put up with it.
"You never play rugby 100pc so you kind of expect it."
As time ticks down on one Irish career and another prepares to begin, Payne knows he can only cope with his own expectations, not those of others.
CENTRES STAGE - CANDIDATES TO REPLACE O’DRISCOLL
Jared Payne (Ulster)
Not qualified for Ireland -- yet. Will do so by next November's international series and the smooth-running, off-loading star is a supreme footballer who could be a real addition to Joe Schmidt's ranks.
Luke Fitzgerald (Leinster)
Has endured a horrific time with injuries, but his significant cameo for Ireland against the All Blacks last month reminded all of his capability in the midfield sector. The 2009 Lion must now persuade Matt O'Connor that he can become a viable long-term provincial replacement for O'Driscoll.
Robbie Henshaw (Connacht)
At 20, Henshaw (left) is the baby of the bunch, but he was parachuted into contention by Schmidt for the November series and was a replacement during the horror show against Australia. Gifted individual who is being earmarked for a lengthy career in green.
Keith Earls (Munster)
In some ways the forgotten candidate, Earls has suffered for his versatility and his early-season performances on the wing for Munster this term have convinced many that his future remains in the back three. However, he may get a chance to re-define that script in Munster once Casey Laulala departs the province at the end of the season.
Darren Cave (Ulster)
Cave ruffled a few feathers -- although not Schmidt's -- with his comments about his face not fitting in the Ireland set-up, even though he first aired such an opinion in Declan Kidney's time in charge. Cave has been in top form of late and has more Heineken Cup try assists -- four -- than any other player in Europe this term.