Speaking to the Official Club Website, Keane said: "The first goal was always going to be vital. I wasn't sure about the decision on the free-kick that led to the goal but I was disappointed in the way we responded to going behind.
"We were a bit naive in the way we just threw men forward and Forest just picked us off as good teams do when you have the attacking options they have.
"We needed to keep it tight for 15 minutes and then go a bit gung ho. We have to learn how to stay in the game.
"Forest showed how far we still have to go but I knew that before kick-off. We have a lot of hard work in front of us but Forest have shown what can be achieved after the progress they have made over the last year."