His lowest point at Barca was their Champions League semifinal defeat to Chelsea.
"We were much better than our rivals but we conceded an unnecessary goal in the return, and before we realised it, we were out. That was a big loss to me, I felt like I could not rise my team again."
Guardiola added: "I left the club because I could not motivate my players.
"If you cannot motivate them, as a coach, you know that the time to leave has arrived."
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