THE History Bhoys have every reason to mark February 8 as a black day for Celtic.
On that date 14 years ago, Inverness Caley Thistle came to Parkhead and dumped Celtic out of the Scottish Cup.
On Saturday, Aberdeen breezed into the same venue and made it an anniversary to forget for Neil Lennon and his players by winning 2-1.
The only genuine connection between the two cup shocks is the date, given the huge difference between John Barnes' Celtic side of 2000 and the one which is currently dominating the game in this country.
Of course, rookie boss Barnes lost his job in the aftermath of the cup exit, while Lennon is as secure as any manager could ever hope to be.
But that doesn't mean the exit from a competition which they were heavy favourites to win does not cut the current incumbent of the Parkhead hot-seat to the very core.
More painful was the manner in which a side which has swept all before it in the league championship - which they lead by 21 points from this same Aberdeen side - capitulated after taking an early lead.
Added to the mind-numbing League Cup loss at home to Morton in September - the only other domestic defeat suffered by Cetic since they were beaten by Motherwell at Fir Park last April - it means all Celtic will have to show for their efforts this season will be the league championship.
The word "all" might seem inappropriate, given that is the biggest prize our game has to offer.
But, having secured the club's 16th league and cup double last season, while marching proudly into the Champions League last 16, it is scant reward and well short of tangible confirmation of how much better Celtic are when measured against every other side in the country.
Be sure that, while retaining the league title was Lennon's No.1 priority, he was shooting for much more than that.
And, while the major departures last summer meant this was always going to be a season of transition and rebuilding, Celtic are strong enough to be able to do this while still collecting silverware.
However, while all eyes were firmly focused on domestic shut-out records and winning streaks, the stat which everyone at Celtic must now face up to is that, for the first time since 1982, they have not reached the quarter-final of either cup competition.
Back then, they were in a state of flux, along with Rangers struggling to contend with a rapidly-emerging New Firm.
Alex Ferguson was about to take his Aberdeen side to league titles, cup wins and European final success against Real Madrid, while Jim McLean was leading Dundee United to heights they had never before attained, including an appearance in the Uefa Cup final, the semi-final of the European Cup, and victory home and away against Barcelona.
Fast forward to today, and Celtic are the only club in the country capable of surviving even the qualifiers for European competition.
So while nothing in life, let alone football, is ever guaranteed, that the Hoops should be winning more than one trophy this season must surely have been considered long odds-on.
Which is why the remainder of the campaign will be clouded in disappointment, for those involved in playing and managing, and those who are paying to watch.
Barry Robson - the former Celtic player who turned architect of their downfall at the weekend as he cajoled his Aberdeen team-mates to victory with goals from Russell Anderson seven minutes before the break and Peter Pawlett five minutes after it to cancel out Anthony Stokes well-taken opener - commented after the match he had never known Celtic Park to be so empty for a game.
There were, in fact, 30,413 in the ground - still the biggest attendance for any of the fifth-round ties - with the top tiers of three stands closed.
Aberdeen had sold out their 3,000 allocation, and their supporters brought with them any atmosphere there was, albeit a number of their songs were distasteful.
If Robson happens to be around on Sunday when St Johnstone are the visitors, he may be given cause to re-assess last Saturday's atmosphere as rocking.
It is going to be a serious challenge for Celtic to keep their fans connected for the remainder of the campaign.
Certainly, they will turn out to see the title confirmed, and that could happen by the end of next month. But what then?
Considering the unbeaten run in the league, and the dominance shown, it would be unfair on this bunch of players if their efforts were not fully recognised as the season was allowed to simply peter out.
However, the onus is on them to excite and entertain a support which has been let down by the manner of their cup exits and the meek way in which the Champions League campaign concluded.
Lennon is determined not to allow the performance level or standards to drop.
To achieve this, he will have to ensure his players recognise displays like the one against Aberdeen are unacceptable, particularly from the defence and midfield.
After all, this was the side which demolished Hearts 7-0 at Tynecastle in the previous round.
Ironically, that will now stand as Celtic's only victory in a domestic cup tie this season.
Since taking over as manager, Lennon has been no stranger to shock cup exits, and the likes of Ross County, Morton, St Mirren, Hearts and Kilmarnock have all enjoyed the thrill of knocking the Parkhead club out.
It does not make this one any easier to take for a man who knows, ultimately, he will be measured by how many trophies he brings to Celtic.
In terms of cups, in his four years at the helm, it is two Scottish Cup successes, and blanks all the way in the League Cup.
So, the sooner his players carry them over the finishing line and deliver a third consecutive championship to Parkhead, the sooner at least some of the pain currently being felt will be salved.