Alan Quinlan: Garry Ringrose must find his feet early as Scotland will be gunning for talented centre on his return from injury
Unlucky No 13 will be feeling heat but he has ability to grasp huge opportunity
The doubts were always there. Am I good enough? Do I really belong at this level? Has my preparation been on point?
Pre-match nerves affect every player differently; they cause some to be physically ill while others are submerged in a trance-like state by the weight of the external pressures.
Confident players are not immune to feelings of pre-match inadequacy - Brian O'Driscoll has talked before about how, crucially, the nerves keep you sharp, how the pre-match meal shouldn't be going down easy into a stomach over-run with butterflies.
It's rare these days, particularly at this stage of the season, for a player to be going into a game feeling 100pc. Knocks, bangs and niggles are inevitable in such a physical sport and playing through soreness is par for the course.
However, if you're making a return to the top level following a lengthy injury absence, particularly after a run-in with a surgeon's scalpel, it's a completely different ball game - mentally and physically.
I had many injuries over the years - I had two plates inserted in my jaw, I broke both my thumbs twice, I had knee and shoulder reconstructions, and I dislocated my elbow towards my final days with Munster - but the returns from surgery were certainly the occasions which caused the most distress.
As you go through your preparations you'll likely have strapping around areas of previous weakness, or you might catch a glimpse of a scar - it all plays on your mind.
And pre-match doubts are magnified if you have been out of the loop for some time, it's only natural.
Your concerns are generally very injury-specific: Can my shoulder handle the contact? What if it pops again? Have I got enough conditioning done on this knee to keep up with the speed of play?
The opposition know your medical history just as well as the lads beside you in the dressing-room and you're expecting to be targeted more than usual when you are returning to the fold.
It felt like there was a bullseye on my left shoulder for the remainder of my career after I dislocated it so publicly at the 2003 World Cup.
Stitches generally heal neatly these days but operations can leave a mental scar that is considerably more difficult to hide.
I never felt as confident using my left shoulder as I did my right after I popped it against Argentina; I still don't have full rotation in it.
That's why attitude is so important with injuries; it's very easy to start seeing yourself as a bit of a victim, asking, 'Why me again?'
In 2003, I felt on top of the world, I was in brilliant shape, I got selected on the Irish team when everyone was fit. It took a while but I had finally reached my Everest.
Then, in one movement, it was all taken away from under me - a reminder that you have to grasp every chance you get.
Garry Ringrose takes to the field today as the white knight of Irish rugby, a humble role model with the tenacity to match his remarkable footballing skills.
He is the third man to partner Bundee Aki in a midfield that has had the mockers on it since Robbie Henshaw went over the Italian whitewash for a second time.
For all of his undoubted ability, Ringrose has played a mere 424 minutes of rugby this season; competitive back-to-back outings against Exeter, and PRO14 games against Benetton, Connacht, Ulster and Southern Kings - the game against the Westerners the exception for not being a cakewalk.
Ringrose will be a star in green for years to come but today he faces one of the biggest tests of his fledgling career.
This time last year Ringrose had never missed a game through injury but as he prepares to win his 12th cap today, the unlucky No 13 does so having gone under the knife three times in the last nine months - on both shoulders and his ankle.
The Scots will be targeting him; they know he will be blowing hard as he adjusts early on and they will be searching forensically for any signs of ring rust.
They'll be assessing how solid he is in contact and how quick he is to change direction, a vital skill for any outside centre in attack and defence.
Ringrose's mind will need to be sharp too; his decision-making will be vital if Ireland are to repel a Scotland side who have serious quality with ball in hand.
His shoulders should be stronger than ever at this stage, and he looked in great shape on his return to Ireland camp, something Keith Earls alluded to earlier this week.
"He just needs a good run now, he looks a bit bigger from the surgery and stuff," Earls said. "He has been doing a lot of weights with his shoulder."
My main concern around Ringrose wouldn't actually be whether he is able to slot straight back in to the Test arena - I think he probably has that freakish quality like a Johnny Sexton or Seán O'Brien to get back up to speed straight away - or whether his ankle is up to it.
When you're coming back from knee, ankle or shoulder surgery, for example, it's the rest of the body that is more likely to let you down.
When I got my cruciate done in 2005 I was moving on a bike again pretty much within a week, but it was so important that the tunnel vision I had for my knee didn't cause me to neglect the rest of my body.
Long gone are the days when you were expected to tog out with your club or with the 'A' team in the province to ease your way back into the fold.
The level of detail in terms of recovery and rehab has changed the perception that you need minutes under your belt to be ready to face the big boys.
However, match fitness remains important, particularly in a game as physical as rugby.
Joe Schmidt may work the players into a state of exhaustion in training to replicate a match scenario but nothing really compares to the white heat of a Test match, and until you make that first tackle and have to drag yourself up off the ground straight away, it's hard to be certain where you are at physically.
In an ideal world Ringrose would have chalked up more game-time in preparation for this, and the likelihood is Chris Farrell would have been starting ahead of the Leinster man had he not picked up a devastating knee injury only days after his man-of-the-match performance against Wales.
Ringrose will hope to settle down early on by getting the ball through his hands and making a couple of tackles.
We know he is an X-factor player but we don't necessarily need to see his array of tricks this afternoon, he just needs to stay on the field for the majority of the game. He can save the show-stopping stuff for Twickenham!
Schmidt is a stickler for detail, we know that, and I'm sure he has weighed up how he would shuffle things were Ringrose or Aki forced to leave the field due to injury or otherwise, as there is a glaring dearth of natural centre cover in the Ireland 23.
Earls could find himself thrown into midfield were we to lose one of our starting centres, yet that would shift our most clinical finisher, who is in the form of his life, out of his best position and into a spot that he has never truly convinced in.
Sexton has played at 12 before, while, interestingly, Joey Carbery has also been given a run at inside centre in the Ireland camp; however with the stakes so high, having no obvious tested solution does ring alarm bells.
Let's hope it doesn't come to that and Ringrose reminds us what we've been missing over the past month.
Then, all going well, he can start to tackle the pre-match nerves for a Grand Slam decider.
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