The Norwegian was reflecting on his side's 3-0 win over Dundee United.
Celtic boss Ronny Deila admitted after his side's 3-0 win over Dundee United in the Scottish Premiership on Sunday afternoon that their first-half performance was one of their worst of the season, according to Sky Sports.
The frank admission came after the Bhoys went into the break goalless with their opponents but then saw Leigh Griffiths net a second-half hat-trick to take them back to eight points clear of second-placed Aberdeen.
In Deila's honest opinion, Celtic have played few halves of football worse than they did at Dundee United this whole campaign.
Which is exactly why he was buoyed by their second-half response.
He told Sky: "The second half was good. We upped the tempo and started to play forward and get some runs and aggression in the team.
"The first half was one of the poorest we have had this season."
To encourage that response, Deila says he had to be direct about his half-time team-talk.
The Norwegian added when asked what he said to the players: "That it was not good enough. You have to really step up and start fighting and win challenges first. The boys answered in a good way."
It's certainly something to think about for next season, as slow starts have cost Celtic this term - both at home and in Europe. On numerous occasions, meanwhile, the Bhoys have recovered from a bad start with strong second-half showings (just like here).
If Deila sorts Celtic's first-half displays out, then, the Scottish Premiership will be looking at an even stronger leading light.