It happens to all great sportsmen at some point in their career. They feel themselves that inch off and realise that they aren't quite what they used to be. Most of us probably can't understand that feeling, when you are so physically supreme that you get paid to be a professional athlete, to express yourself in physical performance, and then one day you find out that the ability you once had is gone.
Brian O'Driscoll is one such great sportsmen and hasn't done too badly for himself since he hung up his boots, forming a career as a highly successful pundit on BT and Newstalk. He was on the latter tonight with Sean O'Brien and was talking about the moment when he realised he'd 'lost it'.
I would still be playing if my legs were still going because I still have a appetite for it, but the reality is that you start doing damage to your reputation and the frustration gets too much when players that you perceive to be relatively average make you look silly.
There was one against Scarlets a few years ago. I can't remember your man's name, he wasn't capped. And he stood me up on the outside and burnt me, and I got an arm on his jersey but couldn't get him down and he went in for a score.
We won the game and we were in the dressing room after the game and I remember being absolutely sick and Joe Schmidt coming over and telling me to cop onto myself, that we'd won the game, that the players don't need to see (O'Driscoll) down after a win.
But I was just disgusted that I had lost that (race) and I could allow that to happen.
And he explained that he had to learn how to conserve his energy as he got a bit older:
It (retiring) happened because I started losing aspects to my game. Particularly from an outside-back point of view, the speed aspect...I was still able to see the gaps but I just wasn't able to get into them as quickly, so I had to become more of a link player and allow that to do my thinking for me.
And play smarter. When your legs go a little bit, and your engine isn't quite how it once was, you have to be able to pull the handbrake up a little bit.
It's strange to think there's some Welsh guy walking around oblivious to the fact that he totally destroyed the confidence of one of rugby's greats - for good.
Having said that, there's no doubt that O'Driscoll caused a fair few sleepless nights himself when he was a younger, quicker BOD.
Listen to the full segment on Off the Ball with BOD and Sean O'Brien here.
We have located the horrifying clip of BOD being skinned. Watch it here - if you dare!