Although a stunning Mario Mandzukic goal ensured Juve were level at the break in Cardiff, Zinedine Zidane’s Real Madrid went on to score three times in the second half to defend their title.
Allegri’s men were also beaten by Spanish opposition in the Champions League final in 2015, with Barcelona 3-1 winners in Berlin, and after tasting defeat for the second time the Italian considered walking away from Juve.
“I left Cardiff with the team and returned to Italy,” Allegri wrote in the Players’ Tribune.
“The next evening, when I got home, I had to ask myself a very hard question: Is this the end of the road? Is this as far as I can take this team?
“I wondered if I should write the final chapter to my story at Juventus. Part of me was thinking about walking in on Monday and respectfully resigning.
“When I got home after that defeat, I had to think hard about whether to continue. I thought about why I had become a manager in the first place.
“I do this because I love teaching. It is truly the joy of my life. I like making players better and smarter.
“So when I thought about this Juventus squad, my decision became quite personal. I know I still have a lot to prove. And I know I still have a lot to teach. So that night, before I went to bed, I decided that if the club was on board with my strategy and we could move on together, then I would stay on.”
Allegri named legendary goalkeeper Gianluigi Buffon – who has never won the Champions League – and striker Paulo Dybala as two key players in Juve’s hunt for the crown.
“For me, I look at Paulo Dybala and Gigi Buffon. In a way, they are the symbol of this team,” he continued. “I see Dybala, like a bright boy about to start his first year in school.
“Buffon, with a World Cup, is about to get his master’s degree. One with his career ahead of him and one near the end. One who wants to show that he can be one of the greats in Europe. One who is already a great, but wants to end his legacy on top.
“I know we can shed the scabs from Cardiff. I know we can have a great season. I know we can have a great Champions League campaign.”