Steve McClaren has admitted his tenure as England manager was a "big failure" and that he thinks about the experience every day.
McClaren told BBC Football Focus: "It could have been one of the biggest and ends up one of the lowest.
"I don't think a day goes by that some aspect of the experience with England doesn't come flashing back to mind and teaching me a lesson, making me move on.
"It was a huge disappointment. I felt, as one would, I'd let down the nation because we didn't qualify.
"However people say it was this, that or the other, the responsibility was mine and mine alone. I had to take that.
"It wasn't pleasant, an experience I don't want to go through again, but it is one that has not quite killed me and makes me stronger."
He insists, however, he is merely getting on with his job rather than trying to prove anyone wrong.
He added: "It is not a road to redemption, it is not to prove to anybody anything, it is really what I do.
"Generally, I have been quite successful at what I do.
"You can't win all the time, sometimes failures come. Sometimes they are big failures and this was a big failure.
"So I moved on and took an opportunity to coach in Europe.
"I am enjoying this experience and probably there is more to come. This is a good, ambitious club.
"How far we can go, I don't know, but you hear the chairman and you'd think we'll go on to win the Champions League."
McClaren has not ruled out the possibility of returning to England.
"You cannot plan a career in football because you do not know," he said. "You roll with the blows and you take it.
"At present I am enjoying my football. Who knows where next but I am happy here."