Steve McClaren admits missing out on the Aston Villa job left him frustrated.
"That [Villa] was a big disappointment," he told The Independent.
"I didn't do my due diligence [on Forest] well enough. I was disappointed [with the rejection from Villa] and wanted to show people. I thought it was a great opportunity - great club, great fans, great history and tradition.
"Unfortunately I knew very early from going in that we weren't on the same wavelength. I was set to move my family [to live near to Forest] and I stopped that one.
"We were the wrong fit. In the end other things were going on behind the scenes.
"For the first time in my life I thought it would be best for everybody, for the football club, the fans, the players of Nottingham Forest... that something had to change. The club had been crying out [for that] before I got there. [For] change in everything within the club. We didn't, by then, have a long-term plan and vision. I didn't have a relationship with the board."