The midfielder's rise and rise brings flesh-and-blood substance to his fellow Norwegian's boasts about his ability to recruit and develop players with a view to selling them on at a tidy profit.
Comparing Stromsgodset, the unfashionable little outfit from the edge of the Arctic Circle who play to crowds in the low thousands, to the global brand which is Celtic might seem rather odd, but in some ways their modus operandi isn't so very different. And by anybody's reckoning, the profit Deila made for Stromsgodset when Johansen was sold to the Parkhead club was a pretty good piece of business.
Deila brought in Johansen and his team-mate Andreas Konradsen from Bodo/Glimt for a combined fee in the region of £100,000. Two years later, Johansen was joining Celtic for £2 million and Konradsen pitching up at Rennes in for £1.5m. It was, as Deila put it on Friday, "OK money".
"Stefan had a hard time before he came to Stromsgodset," Neil Lennon's charismatic successor said. "He was out of the first team at his club and unhappy. Other coaches had given up on him. His career was almost going under.
"I thought 'if we get something out of this then it is a positive and if not it is no problem because there was no financial outlay'. I heard before he came that he had problems with his attitude but from the first day he arrived he worked very hard.
"If you are not in the team you can say it's because the manager is a bad manager, but what you really have to think is 'why am I not in the team?'. Stefan was always patient.
"It took him more than a year to get into the team but he was ready then. He replaced a player who was sold. Since then his career has gone upwards. But he must still work hard to keep getting better. Everyone must take the bar even higher."
Deila does not mince his words when it comes to the harsh reality of selling players on to bigger clubs in the footballing food chain. Indeed, he embraces the concept. "I said to the boys, to Stefan also, 'if you have the possibility [of moving to a bigger club] I am going to drive you there'. It is true. If you make people achieve their dreams, that is what it is all about.
"Of course I want to win trophies, but if you can do something with people so that they progress and fulfil their dreams, then that gives me energy. It someone calls from Barcelona and says they want one of our players then fantastic."
Deila was cautious when it came to commenting on the abilities of the existing Celtic squad, and the topic of potential recruitment.
He has been handed a vast collection of DVDs, video files and statistics to pore over and looks forward to having the club's scouting network - headed up by John Park - at his disposal.
Getting more product from the promise in the Lennoxtown academy is also a strategic priority, but while the Parkhead club have raided the Scandinavian market on a semi-regular basis, Deila hinted he felt there are only a select few from that part of the world who would be able to exist at Champions League level.
"Stromsgodset are a very small club," said Deila, a self-proclaimed disciple of Jurgen Klopp and Brendan Rodgers. "We never had scouts. We didn't buy players. We got them on Bosmans.
"It was a question of talking to the national team coaches and watching football. Now we need players who can play in the Champions League. The players have to have been at that level or are currently at it. Or we need to find players who can be taught to play at that level. You never know where the players will come from."
This was such an assured performance on his debut in front of the Scottish media that it felt almost incongruous to hear Deila confessing to mistakes earlier in his career, ones indeed which have shaped his "humanist" approach to management.
"I've made many mistakes," he said. "One of the biggest was in my first year as a manager when I lost six games in a row. I hope that's the only time that happens. Every match was going wrong and the pressure was harder. I stopped believing in people. I thought I was the leader and the only man who had answers. I pushed everybody away.
"I told them all 'this is not good enough' and it got worse. You have to see a humanistic side to people, to believe they want to perform, want to do well, want to develop -they just need the responsibility. So I learned - I changed it, and they won the week after."
So new age, modern, alien even to the environs of Scottish football. Did Friday feel that it was possible to imagine Deila experiencing some resistance from the more sceptical heads in the dressing room? Those same cynics would say that the mood around Celtic Park will change drastically if the Norwegian cannot successfully negotiate Champions League qualifying, which starts in just over a month's time.
One potential opponent, of course, are none other than Stromsgodset, and it took little encouragement for Deila to mentally change sides of that particular equation. "Before I came here I saw we [Stromsgodset] could draw Celtic and I thought about that," he said. "You always have a chance to win. Always.
"If you are going to go on the pitch and not thinking that then why are you there? But then ... if you are a good team, like we are going to be, you should win games like that."