There comes a point in every season when a journalist bites the bullet and asks a Celtic or Rangers manager - whichever of them is dominant at the time - whether it's reasonable to start thinking about winning the treble. The question is usually couched gently, because the response tends to be something between prickly and dismissive. It is the media's job to ask about a treble because that is what Old Firm supporters start to consider as soon as the cups get going. It is a manager's job to straight-bat the issue away because it can look presumptuous and arrogant even to contemplate it.
There will be no treble for Neil Lennon this season, not after Tuesday night's ugly Scottish League Cup defeat against Morton at Parkhead. There was not even time to put the question to him this season, what with them losing in their very first domestic cup tie. It is increasingly likely he will never win a treble now as Celtic manager. If he is to do so he will have to stay on for at least a fifth full season, which will take him towards the length of service which gets people talking about reaching the end of a modern Old Firm manager's shelf life.
Morton had no need to think about anything beyond their own gleeful celebration of a stunning result in the east end of Glasgow, but their amazing backs-to-the-wall victory served a wider purpose by preserving the exclusivity and specialness of every treble. Since the removal of Rangers as a credible challenger in the two main cup competitions, there have been those among the Celtic support who have blithely assumed that all three trophies would be adorned with green-and-white ribbons and presented as a matter of course.
But if a club and its manager and players are to be celebrated and revered for winning a treble there has to be respect for the rarity and difficulty of the achievement. It is not, and never has been, a routine reward for whichever of the Glasgow clubs gets the better of the other one. Predictably only Celtic and Rangers have ever won it, doing so 10 times between them since the League Cup was introduced as the third major competition in 1946. But even Jock Stein won "only" two. Bill Struth, Walter Smith and Martin O'Neill finished with one each. It was beyond both Graeme Souness and Gordon Strachan. So far it has been beyond Lennon, too. This will be the 10th consecutive season in which the trophies have been shared by at least two clubs. Having to perform to a high standard across a league season, and continually peak for two cup campaigns, is nearly always beyond even the finest teams.
Celtic have underachieved in the cups since Lennon took over. After losing to Ross County, then a first division team, in the 2010 Scottish Cup semi-final, he made Celtic sides that tend to go far in the cups without winning often enough. They have two Scottish Cup triumphs under him but have never lifted the League Cup in four attempts. After six consecutive campaigns in which they at least reached the last four, being bundled out in the third round by a previously struggling Morton side was a wholly unexpected embarrassment.
Lennon knows to expect criticism because it is his job to ensure results like Tuesday's do not happen. It is a stain on his managerial record. But neither his selection nor his tactics were misjudged this week. Eight of the team which started against Morton had played against AC Milan at San Siro last midweek, as did all three of the substitutes he added in the second half. He did not devalue the competition nor underestimate Morton. The only goalscoring absentee was Georgios Samaras, and if Celtic cannot beat Morton just because a single individual is missing they are in bigger trouble than anyone realises.
In Derk Boerrigter and Dylan McGeouch they had two wingers, with Tom Rogic operating behind Teemu Pukki. They had more crosses than a cemetery, more shots than a rifle range. The finishing was generally pretty pathetic and by the end they looked like George Foreman punching their way towards exhaustion. Morton were not playing any sort of cute rope-a-dope game, they were just pummelled, but their impressive defending meant that when they scored on the break through Dougie Imrie's penalty Celtic did not have the craft to save themselves.
The League Cup slipping away, and a potential treble too, was sore for Celtic. Of greater concern were the ordinary performances from Rogic, McGeouch, Boerrigter, Nir Biton and even Pukki, none of whom were in Lennon's first-choice team when the Champions League began in Milan. He needs to be able to rely on his squad men to offer far more. At least they got a game: Amido Balde's omission said it all about the impression he has made since signing for £1.8m.
No-one will give a thought to Morton once attention turns properly towards the visit of Barcelona in five days time, but until then Celtic must like their wounds and mourn how much they lost.