Sliding doors moments. Call it what you will, but the reality is that the difference between a good season and an epic season can come down to one bit of luck – good or bad – or even a dodgy decision.
So, while Celtic are riding high, 12 points clear in their pursuit of back-to-back SPL titles, eyes set on the club's first Treble in 12 years, and with a place in the last 16 of the Champions League topping up the feelgood factor flowing around Parkhead, Neil Lennon still feels the need to sound a note of caution.
The club's return from the mid-season break could not have been more impressive, a 4-1 win over Hearts followed quickly by a 4-0 demolition of Dundee United.
Retaining the championship is now two significant steps closer, as a result.
The effect is to build in margin for error. Any slip-up in future league games will be more of an irritation than seriously damaging to a side set a points target by their manager which requires a winning run all the way to the finishing line.
However, Lennon is also zeroing in on a Treble, and is only too aware that it requires just one bad performance in a cup tie, or even a single lapse in concentration or one moment of misfortune, to make the ambition to repeat the feat last achieved by Martin O'Neill in his first season unattainable.
Which is why, despite the current excellent form of his side, Lennon is anything but relaxed ahead of travelling to Hampden on Sunday where Celtic will face St Mirren in the Scottish Communities League Cup semi-final.
"Every game is a knife edge, in terms of what we want to do domestically and in Europe," explained the Hoops boss.
"And, in a semi-final, anything can happen.
"I am very, very wary of St Mirren and very, very wary of playing at Hampden.
"It will be a totally different environment, different conditions, a different ball, even.
"So we have to adapt very quickly to this game."
You do not need to look too far to unearth the reasons for Lennon's unease at the prospect of transferring Parkhead form the short distance over to the National Stadium.
In March, they headed there as clear favourites to win the League Cup, but lost 1-0 to Kilmarnock.
When they went back to Hampden in April, for the Scottish Cup semi-final, it was Hearts who lay in wait to mug them with a contentious penalty in injury-time.
Lennon is desperate to avoid a Hampden hat-trick of disappointments, and recognises that a rub of the green is an essential requirement on occasions such as this, no matter what form you may be carrying into the cup tie.
"In the League Cup Final against Kilmarnock we played well and should have won, but didn't," he reflected.
"In the Scottish Cup semi- final against Hearts we hit the post twice and it was one of those games where they sat in and got a bit of luck.
"But that is all history now. This is another season, and we want to make playing at Hampden a regular occurrence, and we are going in the right direction."
Celtic will be boosted by the availability of Kelvin Wilson for Sunday's tie, the defender having now served his two-game suspension for the red card picked up retrospectively for an errant elbow in the SPL game against Dundee on Boxing Day.
Lennon is also hopeful Fraser Forster's neck injury will have eased sufficiently to allow him to return to action, though with the Juventus ties looming large, no chances will be taken with the big Geordie.
The plan is for James Forrest to return to training tomorrow, if the progress he has been making in recovering from another hamstring injury continues at the same pace.
But this tie has almost certainly come too soon for the 21-year-old who revels in the wide open spaces of Hampden.
With Efe Ambrose on Africa Cup of Nations duty, and a couple of others still nursing knocks and strains, Lennon will still be without his first-choice starting XI.
But the squad he has patiently built is proving more than capable of coping, as the emphatic wins over Hearts and Dundee United underlined.
"When you consider my first-choice keeper, my two first-choice central defenders, as well as Kris Commons, Paddy McCourt and James Forrest have all been missing, we are doing well," said Lennon.
"The players are feeling the excitement, they are feeling the buzz they are getting out of their football.
"They are enjoying it, playing with good players. They are all in a very good place at the minute.
"But it can all change very quickly, so you have got to temper it sometimes.
"To be fair, we have had a lot of highs, but a few lows as well, so they are well experienced in both."
Not that Lennon would ever allow complacency to infiltrate the Celtic camp and undermine all the hard work which is being put in.
There is always room for improvement, even after sweeping away a side like Dundee United by four clear goals.
"If we defend like we did at times on Tuesday, we will get punished," is Lennon's reminder.
"Credit to the squad. It's strong, and the players are all trying to peak for the Juventus games.
"But every game is precious and every game is important.
"If we don't turn up on Sunday, St Mirren could turn us over and the chance of a Treble would be gone.
"It's very exciting that we have put ourselves in this position, but one game could change everything."