The Norwegian revealed he has clashed with every member of his squad at some point and says the response from some of them has disappointed him.
But Deila believes he has now successfully got his message across to the majority of those under his command and is confident Celtic are gradually feeling the benefit of his methods.
“I can’t see one player here who I haven’t had a confrontation with,” said Deila. “But that’s good, because a culture without confrontation is dead. A marriage without confrontation is dead. If you have the same problems all the time, then you have to give up.
“Not everybody has reacted as I would have wanted to these confrontations. But I treat them with respect and I have given everybody a chance and never give up. But sometimes you have to take decisions because this is not a kindergarten, it’s a high performance team and we have to get results, so you don’t have time to wait for everybody all the time.
“Here you have to learn quick and that’s something that has to be in the back of their minds.
“When you have competition for places, you can stretch them and that’s why so many players have been in the team and then been out for a little while but then they are back again and they are improving. So it goes in circles and I think we are slowly going upwards.”
An obvious example of someone who has flourished under the challenges posed by Deila is Nir Bitton. The Israeli midfielder was unable to command a first-team place at the start of last season but has now become one of Celtic’s most valuable and influential performers.
Others have remained out in the cold, such as Anthony Stokes. The Irish forward has made just one starting appearance this season and even remained an unused substitute for Wednesday night’s League Cup tie against Raith Rovers which saw 18-year-old Aidan Nesbitt sent on ahead of him to make his debut.
“With Nir, last year I didn’t understand where I could use him,” reflected Deila. “He was not giving me anything but again we had a very good talk and he understood what I wanted and he started to do it. Now you can see what kind of improvement he has made.
“I accept everyone does mistakes and does good things, but I ask how much do you learn from mistakes?
“If I have to have the same conversation with him five times in five months, then you give up. Those players are finished at Celtic because they can’t handle the way it is going.
“The others are improving and one man can’t afford to stand still. That player might have been good enough at one point but it won’t stay that way. In the dressing room after the game on Wednesday night, I congratulated Aidan Nesbitt on making his debut and then asked him why he had been given it. He said he didn’t know, so I told him it was because he had earned it.
“He had shown enough in training and had also scored four goals in three games for the under-20 team. When you have maybe five players ahead of you in the queue for a place in the team, you have to believe in yourself.
“The younger players now train with us three or four times a week and they are not afraid to be there, they really like to be among the top players and they start to understand ‘I have a chance here’. That’s the culture we are creating and it will come. I know it will come.”