Berger said: "We had a meeting at the during pre-season, then another meeting a few months after that, and it just didn't work out. After that I realised I would be leaving at the end of the season.
"It just didn't work. In the meeting they had different ideas, I had different ideas. It just didn't work out."
He added: "What I've learned is one year you can be the hero and the next year you can be the victim. Even if you sign a contract, for example for three or four years, you can't say, 'I'll be staying here' as anything can happen such as injuries, bad results and a new manager coming in.
"I never thought I would have stayed here for seven years. I would love to stay here but that's not to be the case so I have to move on. I'm looking forward to the new challenge."