Liverpool were better in all areas - Klopp
Last season's Bundesliga runners-up were soundly beaten on Sunday by the team who finished second in the 2013-14 Premier League.
Early goals from Daniel Sturridge and Dejan Lovren put Liverpool in complete control at Anfield, before Philippe Coutinho and Jordan Henderson added further goals in the second half to complete a comprehensive home win.
Klopp made no excuses for his side's poor performance, but is hoping Dortmund can take positives from the game as they prepare for Wednesday's DFL-Supercup tie with Bayern Munich and the start of the DFB-Pokal and Bundesliga campaigns.
"The first goal saw us leave a gaping hole; the second was a free header and to be fair we were a few percent short in all areas. That's why we got a drubbing and why it hurts," Klopp told Dortmund's official website.
"Where we are right now, our opponents were just too good for us. The physicality Liverpool were able to bring to the game just isn't there for us just yet.
"If you draw the right conclusions from results like this then it can only be positive. There were no points on offer but we won a lot of insight.
"We are still in the heart of pre-season, and we always put a lot of physical effort into our pre-season which benefits us as the long season progresses, and so results like this can happen."
Dortmund midfielder Sven Bender believes lessons can be learned from Sunday's game.
"It should act as a wake-up call and make us focus on what we have to do," he added.
"It is going to get a bit hectic now but we know we are not the kind of team that should lose 4-0 in pre-season no matter how well our opponents play.
"We certainly expected to do more but we just couldn't get started. The result is a fair one. It's just good that there weren't any points at stake."
Meanwhile, Dortmund announced on Sunday that Germany defender Mats Hummels will succeed Sebastian Kehl as club captain, with Marco Reus and Roman Weidenfeller serving as his deputies.