The Reds, who are seventh in the Premier League table, have now own only once in their last six league matches.
"The result is disappointing, but the most disappointing thing for me was that I don't think we were ready to play the game," Dalglish told reporters. "I don't think the approach was correct and I don't think the way we went about our work was correct.
"If they needed a lesson to be taught to them then today was it. If they think they can just turn up and get a result, not be as competitive and not match the opposition for effort and commitment then they've got a lesson today.
"If they've learned it then fine. Without trying to take anything away from Owen [Coyle] and the way Bolton played, we have to look at ourselves and see what we can do to try and prevent it from happening in the future. That's what we'll do."
Liverpool travel to Manchester City on Wednesday for the second leg of their Carling Cup semi-final.