The 48-year-old was dismissed from his post in November following the team's disappointing performance in the 2014 World Cup qualifying campaign.
"I found the international scene quite difficult - if something went wrong, you had to wait a long period before you could do something about it," Sky Sports News quotes him as saying.
"I found that incredibly frustrating. And then of course you get to the next game and you are missing five players who played the previous game.
"I'm methodical with the way I work, I like to have the players on a weekly basis, play the game, do the analysis and prepare for the game on a Saturday, and it becomes a routine.
"I could never really get into a routine I was comfortable with. On saying that, I wouldn't swap any of it, even the kicking I got towards the end. It's all character-building and I was hugely proud to be national team manager."