Most importantly, only one trophy has been collected at the National Stadium, despite three finals having been contested.

That hurts, but not as much as the fact the club, to a man, are convinced that it has been performances not of men in Hoops but men in the middle which have caused them so much heartache and pain.

The 2-1 defeat by Hearts in the William Hill Scottish Cup semi-final is just the latest dagger in the back.

With it went the hope of a SPL championship and Scottish Cup double, just as the dream of a rare treble had disappeared on their last visit to Hampden when Kilmarnock provided the shock with a 1-0 win in he final of the League Cup.

Defeat in any major game cuts to the core, and the pain stays with players, management and supporters alike for years to come.

When dubious refereeing decisions rub salt into the wounds, the cries of anguish are only amplified.

In the League Cup final, it was Willie Collum who bore the brunt of the Hoops' anger after denying a penalty when Anthony Stokes went down in the box late in the game under a Michael Nelson challenge from behind.

Yesterday, it was Euan Norris who stole the show – ending Celtic's double ambition in the process – with his take on the handballs in the two boxes in the dying minutes.

It would have been much easier for the referee to wave away both claims as there is a strong case to be argued for the fact neither Victor Wanyama nor Andy Webster could reasonably be expected to get their hands out of the way of the ball from such close range.

The fact Norris gave Hearts a penalty – despite allegedly telling Celtic players it was because the ball struck the hand of Victor Wanyama after bouncing off Joe Ledley – but elected to ignore Hoops claims for handball against Webster only adds fuel to already smouldering resentment within the Parkhead camp that they do not get a fair crack of the whip when it comes to big decisions.

And the fact that Gary Hooper's equaliser could have been ruled offside had the main stand linesman, Willie Conquer, been more alert does nothing to dilute the belief within Celtic that the men in the middle are having too big a say – and a negative one at that – in determining the outcome of on the big occasions.

Of course, the age-old argument that, if they took their chances, Celtic could afford to ignore such intrusions, does hold good.

And Ki Sung-Yueng will know that, had he hit the target and not the post when presented with excellent opportunities in each half, all the drama at the end would have mattered much less.

It must be galling for the Celtic management team that their players have created more than enough chances to win this semi-final and the League Cup final before it.

And, as the top scoring side in the country, buoyed by the collection of the SPL title just eight days earlier, it is yet another inexplicable mis-fire in a season when shooting themselves in the foot appeared to be something they had purged from their arsenal.

Coach Alan Thompson felt the pain in the dressing room after the match, and will make it his responsibility – along with the rest of the backroom staff – to analyse what went wrong, and put plans in place to make sure it does not bring their triumphant season to a shuddering halt.

The road to recovery has been walked plenty times in the past two years, and always the squad has emerged stronger for the experience.

Thompson said: "We will just approach it as we have done after all these games. We are not disappointed in any of the performances, really.

"Maybe the League Cup final last year against Rangers we didn't quite get at it.

"But, apart from that, the final against Kilmarnock we were happy with the way, albeit we missed chances.

"And yesterday, we were happy with the way we played, but missed chances again."

Thompson is in no way attempting to downplay the significance of the defeat, and acknowledged that, had Ki converted the first of his gilt-edged chances, the complexion of the game would have been different.

He said: "It was a big one, and it is just disappointing we have lost a game we believe we deserved to win. But, decisions, and big ones, have cost us again."

It was not just the penalty calls which upset the Celtic squad. The decision only to yellow card Ian Black for his first-half foul on Joe Ledley which Thompson claimed could have left the midfielder with a broken leg, was another bone of contention which added to the belief that the referee's performance had not matched the occasion.

The fact the same player escaped a second yellow after clearly handling the ball deliberately would only have added to their ire.

"I have seen the tackle, and it is a bad one," said Thommo. "It's over the ball. It's over the top. Joe's quite lucky he has got away with it, and he gets a yellow card for it, which, in my opinion is wrong.

"But, there you go, can't change it now."

Like the result, itself. Now the challenge is to control the feeling of injustice, no matter how compelling, and ensure it is not allowed to overwhelm the feeling of achievement which should be swamping a club who have brought the SPL title back to Parkhead for the first time in four years.