Bayern Munich striker Robert Lewandowski has explained at length why Jurgen Klopp was like a "bad teacher" to him during the time they worked together at Borussia Dortmund.
The Polish forward struggled to get going in Germany after he joined BVB in 2010, and was even used in an unfamiliar No. 10 role at times, while he was also believed to find training under Klopp difficult.
Lewandowski reportedly confronted his former manager to ask the German what he wanted from him, which led to a conversation that would change his style of play and kick start what has been an incredible career.
"Jurgen was not only a father figure to me. As a coach, he was like the 'bad' teacher. And I mean that in the best sense of the word," he told the Players' Tribune.
"Let me explain. Think back to you when you were in school. Which teacher do you remember the most? Not the one who made life easy for you and never expected anything from you. No, no, no.
See below where Lewandowski ranks among the leading goalscorers in Europe's top five leagues this season so far:
"You remember the bad teacher, the one who was strict with you. The one who put pressure on you and did everything to get the best out of you. That’s the teacher who made you better, right? And Jurgen was like that.
"He was not content to let you be a B student, you know? Jurgen wanted A+ students. He didn’t want it for him. He wanted it for you.
"He taught me so much. When I arrived at Dortmund, I wanted to do everything quickly: strong pass, one touch only. Jurgen showed me to calm down - to take two touches if necessary. It was totally against my nature, but soon I was scoring more goals.
"When I had that down, he challenged me to speed it up again. One touch. BANG. Goal. He slowed me down to speed me up. It sounds simple, but it was genius, really."
Lewandowski scored 103 goals in 187 matches for Dortmund, winning four trophies, including two Bundesliga titles before joining Bayern Munich in 2014. A year later, Klopp succeeded Brendan Rodgers at Liverpool.