The Italian was forced to retire at the age of 32 because of knee injury that he sustained while playing for the Blues.
When asked what made him backtrack and decide to move into management, the 42-year-old told the club's official website: "People change. I don't know what it was, age perhaps. I was still playing then.
"When you're a football man you are hooked, it's like an addiction. You can live without it for a little while but the addiction is always there, and I just felt at some point that I wanted to live those moments during the week where you are tense, you feel the adrenalin and the emotions that you don't get in another job.
I've had it all my life and I can live without it for a little while but it's always there, I had the fire in my belly again and wanted to do something in football.
"I still had a great time doing other things. There is a time in life for everything, and it was the right time for me after my injury to finish that chapter in my life, get away from it and then begin a new one.
"I think it helped me. It gave me some balance, but I didn't see coming back into football as unfinished business. I was very happy with my career. Some people finish their career with age, some others with injury and others with their own decision. Everybody is different but I never felt like it was unfinished business."
Chelsea won the Champions League and FA Cup under Di Matteo's guidance last season.