For all of Robbie Keane's durability, instability has coursed his career for club and country.
From the strife that undermined his brief spell at Inter Milan, or the begrudging diffidence that was associated with his Liverpool career, certainty has been absent for lengthy periods.
For Ireland, the stellar beginnings that produced a gifted European Championships-winning youth side and an impressive debut at a major tournament hinted at what he expected to be a garlanded international calling.
His goals tally -- for club and country -- is testament to a defiance of spirit that has railed against his critics. But he is the first to concede that the barren periods that followed Ireland's last appearance at a major tournament a decade ago failed to fulfil his expectations of what life might be like as a senior international.
Now, so many years later, this is his moment. A little older, a little wiser and, perhaps, a little chubbier, Keane appears ready to announce his presence, maybe for the last time, on the world's biggest stage.
He's 31 now but the burden of duty seems to hang a little lighter around his neck than at any time before.
"There has been a lot of responsibility on my shoulders since I was 17," he said yesterday.
"That hasn't changed since then. People look at me to score goals and now I'm captain there is a big responsibility to help the team as much as I can. But I just have to concentrate on my own performances and lead by example."
His own performances will define his team's venture over the next fortnight.
Lacking form in the outrageously fabricated exercise that is the MLS, Keane arrives at this pivotal moment in the twilight of his career in indifferent shape. Not that he will admit to such doubts.
"I feel fine," he says. "The last couple of weeks have been very good. We had the week in Malahide getting lads back together.
"Through that first week doing all the stuff we had to do outside of football, it's been good that this week's been fully concentrated on training.
"The lads are fit and sharp and on the training ground every day and I have seen that the sharpness of every player has been very good. This week now is where it starts. It was good to get 45 minutes the other night. I feel fine."
Ireland's supporters will dearly hope that is the case. As one of Ireland's indispensable players, it may be unlikely he will get a full 90 minutes tonight. Next Sunday, his manager may not be able to afford such a luxury.
If there remain obvious anxieties amongst his most fervent supporters for Keane's physical welfare, there is little sign of mental anguish despite his long wait to reappear on one of football's significant stages.
"Yeah of course, I've said it before but you take things for granted when you're younger. You always think that you're going to be in every tournament.
"It certainly does feel different this time. There has always been a great team spirit in the Irish camp, but for some reason this has been a little bit different.
"It's the group of players, how well they get on with each other, it's been brilliant. There have been no little niggles which you usually get in tournaments like this when you're together for a long time. Obviously 10 years ago there was a couple..."
Oh, how we can laugh about it now. Keane's oblique reference to the build-up has a primary source: the unyielding influence of his iron-fisted manager, evidenced yet again in a playful but, at the same time, suggestive segue.
Asked to plamas the man sitting beside him, Keane began to speak before his manager interjected excitedly with a nudged, "Balance!".
"Well," continued Keane, "there you have it. Balance. He says it himself, how can I argue with that? I want to play next Sunday."
The audience erupts. It is 'Steptoe and Son' with all the hatred pared down to a minimum; Il Capo and El Capitan, as the manager likes to call him.
The strength of purpose that exists in this manager/captain relationship is like few others Keane has been able to call upon during his lengthy career.
It has imbued in Keane a sense of calm whose only qualities can be tested by their emergence in the hard currency of goals.
"I mentioned before the Estonia game, that relaxed feeling we had before that game and it is very, very similar to now, to be honest," he says, spurning talk that his side are outsiders, as if quietly confident that others may underestimate Ireland.
"The intensity in training has been brilliant, but around the place people don't seem to be uptight or worried about next week. And I think that's always important as a player to have that calmness about you.
"Certainly over the years, the way I play better is when I keep calm. When I started getting myself worked up too much about things, you end up doing stupid things, stupid running. So far the calmness around the place has been very good."
It is a certainty that admits little doubt. A certainty upon which Keane can only profit if his body is as sharply focused as his mind.
As the man from Sky twittered excitedly about the extraordinary precedent set by the manager in effectively announcing his Croatian combatants seven days in advance, anyone who knows this Ireland squad were a little less unnerved.
Such stability underpins Trapattoni's Ireland; when Keane first captained Ireland, anarchy was king.
"The players are getting better with every game, more comfortable with international football. We've had the same starting XI for some time now so the players are very, very comfortable with each other.
"And the players on the bench who come on, they know exactly the role they have to do. And for a player that's very, very important to know that."
Certainty and stability will guide this Irish team. To where? Keane doesn't dismiss Marco Tardelli's fanciful predictions of a day earlier.
"I hope it is a dream that comes true," he smiles. Now he awaits their translation into a daring reality.