Leinster head coach has described the loss to Glasgow as a frustrating days but he will try to look to the positives ahead of the Heineken Champions Cup semi-final against Toulouse.
Glasgow ran in five tries as they defeated the reigning Guinness PRO14 champions at RDS to move to the top of Conference A, becoming the first Scottish time to win at Leinster in eight years.
While he believes Scottish side were deserving of the win, Cullen believes his side took their foot off the gas during the second half and lacked cohesiveness on a difficult afternoon.
"We stood off a bit too much, especially in the first half. We had a strong breeze behind us that we just let Glasgow play. I thought we were just a bit passive, it was disappointing," he told eir sport.
"I thought we showed a lot more energy at the start of the second half but it's like we took our foot off the gas and allowed Glasgow back into the game and I thought they were very strong, capitalising on all the opportunities. They were very deserving of their win.
"We chop and change our team quite a bit so sometimes it makes life difficult for us and we lacked that bit of cohesiveness to go forward together as a group in terms of our line speed and defence. Glasgow are such a dangerous and we made them look good out there. It's a good experience for a lot of players.
We'll take plenty of bits from the game, it's a time for reflection. It's a long week before we play Toulouse at the Aviva Stadium."
Leinster host Toulouse at the Aviva Stadium in the Champions Cup semi-final on Easter Sunday and, while the defeat was not the ideal preparation for the game, there were some positives for the Blues as both Dave and Rob Kearney scored twice, while Devin Toner and Robbie Henshaw made their return from injury.
"There were some positives - Dev coming back and got through 80 minutes, Robbie got 60 minutes and Sean O'Brien got 60 minutes. Some pleasing bits but overall a pretty frustrating day," Cullen added.
"We just lacked that bit of cohesiveness" @leinsterrugby Head Coach Leo Cullen felt his side 'took their foot off the gas' during their defeat to Glasgow at the RDS this afternoon. #GuinnessPRO14 pic.twitter.com/6aCXgviFzF— eir Sport (@eirSport) April 13, 2019
Leinster play Toulouse in the Heineken Champions Cup semi-final at the Aviva Stadium on Sunday, 21 April live on BT Sport 2 on the eir sport pack [kick-off 3.15pm]. Subscribe here
Image: Inpho Photography/Ryan Byrne