As he picks through the crumbs of another ultimately fruitless Champions League night, Neil Lennon knows he's got to find that missing ingredient - and quickly.
Against Barcelona, they created three decent chances, better, even, than the ones they made in the San Siro against AC Milan on match day one.
However, they failed to take any of them, and another two blanks are added to the pair they registered in the last 16 matches against Juventus in February/March when they still had Gary Hooper, Victor Wanyama, et al.
Sure, there is consolation to be taken from the fact they knocked in five in the opening qualifiers against Cliftonville, another to edge out Elfsborg, then three to peg back Shakhter Karagandy in the play-off.
But against the real elite in the competition proper, they have hit a wall - and it is hurting them badly.
Bottom of Group H, with their points tally matching their goals, the need to break this sequence is pressing.
When Ajax come to Glasgow in three weeks, it is essential the Hoops get a win, and, of course, to achieve that, they have to score.
Lennon can't fault his players for their effort and praises them for creating the chances they have against two of Europe's best.
But, he is honest enough to concede that getting 99% of the game right is not good enough, if that final 1% is the vital element.
The Parkhead boss knows the danger inherent with regularly coming close to achieving a good result, only to be left deflated.
And he has made it clear to those in the dressing room who are wondering what it takes to turn good performances into results that the answer is staring them in the face.
"We need to score goals, we need to take our chances," said the Parkhead boss. "You don't get many opportunities at this level, so you must take them when they come along.
"It's the difference at this level, or any level, really. You always know chances are going to be a premium in these games, but they were good chances we made against Barcelona.
"We played well, though I felt we lacked a little bit of belief on the ball in the first half. In the second, we were a lot better and that's when we had a couple of good chances to score.
"There wasn't anything in the game. We knew they would have the lion's share of possession, which they did, and which is no disgrace because that's what they do.
"We defended comfortably, and I felt the pace we had in the team dealt with the majority of what they threw at us. But you have to score, and that's the disappointment."
The best chances fell to James Forrest and Charlie Mulgrew, the former seeing his powerful drive from a Virgil van Dijk knock down well saved by Victor Valdes, and from the resulting corner the latter contrived to fire his header down but wide.
Like the Anthony Stokes free-kick which clipped the bar in the San Siro, these are the fine lines between getting something from these games and being emptied. However, Lennon is relieved to see that, despite their unrewarded start to the Group H campaign, the heads are not down.
The mitigating circumstances of losing captain Scott Brown for the final half hour of the game against Barca and the suspension which will follow has made the Hoops players who will be in contention to face Ajax all the more determined to begin playing catch up on those occupying the last 16 and Europa League places.
No one epitomises this better than the man who took over the armband from Brown on Tuesday, Georgios Samaras.
He had looked every inch on a par with the artisans of Barcelona before Brown's removal. But, the red card took his game and commitment to another level.
Lennon said: "He's a very good player. We ask him to do a lot, and he gives us everything. He had our best chance in the first half when he burst through and forced Valdes to come out and block.
"Their keeper also had a great save from James later on. He had just come on and did wonderfully with his shot. There is nothing you can do about that, it was just a world-class save."
Lennon took consolation from the fact Forrest is now back in action, his substitute appearance his first for the club since scoring the vital third goal against Shakhter in August.
And there is more good news coming along, as the Celtic boss explained. "I'm hoping Joe Ledley will be back soon, and we are trying to get Nir Biton up to speed. He wasn't feeling well on Tuesday morning, but was well enough in the afternoon to take a place on the bench.
"Beram Kayal has missed a bit of football, but managed to make his return on Tuesday as a sub. We will need to get all three up and at it otherwise, if Scott is suspended, we will be short in that area of the team."