"I didn't understand what I could achieve in the game at that time, I didn't really take football that seriously. I wasn't a bad lad or anything like that, I just didn't appreciate how good football could be for you.
"But when I got to around 20 I realised that I could really do something with my career. I went out on loan to Forfar and that's when a switch went off inside my head and I thought 'wait a minute Barry, you're better than this'. I suddenly knew my career could go a lot further than that. The Inverness manager at that time (Steve Paterson) felt it would help my maturity to go to Forfar and it did. I went down to the third division, did well, and took it from there. That's when I got my head down, started working hard and made sure I got back to the top.
"I've only just turned 29 and I've looked after myself well. I've lived my life right and that will hopefully help me play on well into my 30s. Every pre-season I come back, I feel stronger and better. That's just down to eating and drinking the right things.
"It has been unbelievable hard work to get to where I am now, but it's going to be even harder to stay there. I look forward to the challenge at Celtic and I believe I can do well here."
He is confident he can adapt quickly to the demands which surround an Old Firm player.
"I won't be overawed by it," he said. "I know what it's like to play at Parkhead, although I don't know what it's like to play here for Celtic. It's better playing in front of 60,000 people than in front of six. If you don't have that ambition to better yourself and move on to a higher level, then I don't think there is any point being a football player. I told Craig Levein that at the time I signed my last contract with Dundee United. They are a fantastic club, but I wanted to play at the highest level possible.
"This is a big leap in terms of the size and prestige of the club I'm joining, but Dundee United are still a big club and I had a bit of added pressure there as captain. Hopefully that will stand me in good stead for coming here."