Quite simply, Andrew Strauss knew it was someone else's time.
He won't have taken the decision to give up the England captaincy lightly - it is a massive decision after all - but when you know, you know. Very quickly it hits you and you realise that you are done.
Strauss said he knew that he'd run his race and that's exactly how I felt when I resigned in 2003. I knew it was time for someone else to take over. For me it was so clear that it happened just one Test into a series with South Africa.
The timing of his decision makes sense; he ended his Test career where it began, at Lord's, after his 100th Test, 50 of which have been as captain.
He's been in charge for the most successful period English cricket has ever had and should be very proud of his career and what he's achieved. He's been an unbelievable leader.
I know England are having a difficult summer against South Africa but you have to judge Strauss on his reign as a whole and to win the Ashes at home, and then retain them in Australia and go to number one in the world is truly some achievement.
There's a lot to learn from the way he's led the side, too. He's been a very dignified leader of the country; you are an ambassador for your country as an England cricket captain.
It's never been about Andrew Strauss, to be honest. He's never put himself out in front because players pick up on that.
Your team-mates pick up on that if you are giving it the big 'un - 'it's all down to me' - and he has never done that. It's always been about the team - he always stays behind the scenes in a very dignified manner.
I know every England cricket fan will be proud that Andrew Strauss has been our cricket captain. He's led us to a lot of glory and a lot of success.
I think Strauss would have made his decision whether the Kevin Pietersen saga had happened or not.
If he was still smashing bowlers around, scoring hundred after hundred and England had walloped South Africa 3-0 then he probably would have stayed - why should he not try to continue the work that he's done so successfully?
But he felt that his batting was sliding away; he hasn't played particularly well over the last year or so and as a leader and a captain you want to play well because you're asking the same of other people.
If you're not, that wears you down mentally.
Nevertheless Strauss will have mixed emotions in the weeks ahead.
He'll experience a small sense of relief because the job of England captain is all-consuming - it takes over your life.
It's a great job, don't get me wrong, and being a professional cricketer is a fantastic career but it does take its toll.
On the one-hand he had technical issues to worry about and work on, just like any other player, but every day as a captain you think about your team and where they are going and what they're getting up to.
Inevitably any issue with English cricket ends up at the captain's door; that will now stop for Strauss, so there will be an element of relief. There will also be pride in what he's achieved - over 7,000 Test runs for a start.
A few weeks after I quit, I felt a sadness that the job was no longer mine. The fact that you've given it away makes no difference.
When you wake up that first morning that you are no longer England captain, there's a part of you that thinks 'crikey, I miss that already' because it is a special part of your life.
The most important thing is that he doesn't strike me as anyone who has any sort of bitterness; he's just going to move on. He's a well-rounded individual and there are other things in his life that he can now pursue.
He's a bright lad and I wish him well for the future.