In the seemingly eternal battle of attrition that is life with the Old Firm, a player is often in one of the situations that faced soldiers in the First World War trenches, though obviously they never suffer the horrors that the troops endured back then.
In the trenches, no soldier would ever take the third match to light his ciggie, the reason being that snipers opposite would spot the first flame, use the second light to take sight and the third to blow your head off.
These days in the Old Firm, you are usually allowed three big mistakes - sometimes less - before you are dropped, and Celtic's Glenn Loovens is presently on his third light, metaphorically speaking.
His own goal against Rangers last Sunday, followed by his dreadful error to allow Sam Parkin to score St Johnstone's first goal on Wednesday have put the big Dutchman on a warning as to his place in the Celtic team, as his manager Neil Lennon confirmed yesterday.
With players coming back from injury and Daniel Majstorovic putting in a good shift at McDiarmid Park in the Co-operative Insurance Cup quarter final, Lennon can now pick from Loovens, Thomas Rogne and Joos Hooiveld to accompany the giant Swede in the centre of defence.
"Joos has been fit for the last couple of weeks and Thomas is fit now," said Lennon ominously, "so there is plenty competition there if we feel the need to make changes."
That being said, Lennon is confident that the former Feyenoord and Cardiff City defender has the mental strength to come through this sticky patch.
"He has been pretty consistent up until a couple of weeks ago," said Lennon. "I've been pretty happy with his form, but when you are in the spotlight in the Old Firm and you make individual mistakes you are going to take some criticism."
Lennon does not want one man to take the blame for the problems which Celtic experienced against St Johnstone, faults that may lead to personnel changes when the two sides meet on SPL business today for a High Noon showdown in Perth.
He said: "We made it difficult for ourselves because at 3-0 we were cruising, and it could have been four, but from the free kick we have conceded a really poor goal and Gary Hooper missed a couple of really good chances to see the game out.
"Attacking-wise I was very pleased, we counter-attacked very well with pace, vigour and a bit of quality, and we defended the set pieces in the main very well, but it's a new environment for a lot of the players and maybe they haven't seen that type of football before when teams are pressing and playing a physical style of game."So for them to come through that relatively unscathed is great but they are going to have to do it all again.
"It's an advantage that the players have seen on Wednesday that St Johnstone are well prepared, so they know what is coming to them.
"We might make some changes - might, because I'm not sure about that yet. We have to analyse the game again and discuss it. We have conceded five goals in three games now, and that is a concern for us. No one's place is guaranteed."
Failure to adapt to Wednesday night's conditions - weather, pitch and opposition style - may be one of the criteria by which Lennon judges fitness for purpose, in which case Majstorovic, goalkeeper Fraser Forster, Gary Hooper and goalscorers Niall McGinn and Anthony Stokes can rest easy about their inclusion in the squad, as they were singled out for Lennon's praise, as was Georgios Samaras in an unexpected role - "he got back and defended set pieces pretty well for us."
Irish international Stokes is another who "bounced back" from his under-par display against Rangers, said Lennon.
"He is a bit of a maverick of at times, he's a very instinctive type of player and we like his qualities, but we just want him to fit in to the team shape at times a little bit better.
"He's a goalscorer, but he's got more to his game than that. He has made a good start."
Lennon revealed that striker Gary Hooper had a precautionary x-ray on a foot injury after the St Johnstone match, and both he and Shaun Maloney, who injured an eye against Rangers, will be assessed this morning to see if they can play.
Celtic will definitely be without James Forrest whose inflamed ankle will be allowed to settle down before he is risked, and also Scott Brown and Biryam Kayal who are four to six weeks away from playing, while Daryl Murphy will be out for another fortnight.
There were some who criticised Lennon for the amount of players he drafted in during the summer, but injuries have told on the squad, and his judgement on numbers, at least, has certainly been proven correct.
St Johnstone manager Derek McInnes expects to name a similar side to the one who lost to Celtic midweek.
Murray Davidson took a knock to his ankle but should be fit as Saints attempt to make amends for their Co-operative Insurance Cup exit. Graham Gartland and Kevin Moon (both knee) and Jody Morris (rib) are still all out.
l Today's match is subject to a 9am pitch inspection because of heavy rainfall in Perth over recent days. A St Johnstone statement said: "Although the weather forecasts strongly indicate that the rain will clear and not return, the club have arranged a precautionary inspection to keep any inconvenience to supporters to a minimum in the event of a postponement."