Can, who marked his first start for Dortmund with a stunning long-range goal, said they only had themselves to blame after conceding twice in the dying stages to stay third, three points behind leaders Bayern Munich.
"When we take the lead, we have to be a little dirtier," said the midfielder, who joined last month from Juventus.
"That's something the team has to learn, defensively we all have to be better together. It was definitely a setback, but anything can still happen."
Dortmund were 3-2 up going into the final 10 minutes thanks to goals by Mats Hummels, Can and Raphael Guerreiro.
However after Kevin Volland netted two first-half goals for Leverkusen, substitute Leon Bailey swept home to make it 3-3 on 81 minutes before playing a part in Lars Bender's headed winner.
There was just 82 seconds between Leverkusen's final two goals as the Dortmund defence was caught napping.