To continue playing late into your twenties in the same style that you once played as a teenager is not possible.
— Paul Scholes
If I was to become a manager, I would not want someone else to be signing the players for the team that my job depended on.
Managing a club like Oldham has to be an all-absorbing, seven-days-a-week commitment.
A cup final is all about seizing the moment. You cannot put right a mistake or a missed opportunity the following week.
When I started as a pro at United, I played alongside Bryan Robson in the A-team and later in the senior side. With Bryan, it didn't matter what level we were playing or which one of his team-mates got kicked. Within five minutes, you could guarantee that the opponent in question would be in a heap on the floor, courtesy of Bryan.
There is no doubt that my former manager Sir Alex exerted an influence over some referees. He was the master of dropping a comment into his Friday press conference - for instance, how long it had been since we had been given a penalty, or the treatment meted out to a player like Cristiano Ronaldo.
Messi is as famous as any footballer has ever been, and yet, when it comes down to it, we don't know much about him. I read that he is a family man and likes to walk his dogs, but beyond that, he's a mystery, really. I like that.
Martin Skrtel is good at rattling the opposing centre-forward.
United are about attacking football, and everything else has to takes its place behind that.
As a midfielder at United, I had to pass the ball forward, and yes, it did not always work. It did not always mean putting a chance on a plate for the strikers. It was up to them to get on the ball and score goals. Was it easy? No, but we were playing for United. It was not supposed to be easy.
If you want a measure of how private a place the dressing room was when I was growing up at Manchester United, consider this: even Sir Alex Ferguson would knock before coming into the dressing room at the Cliff, the old training ground. The dressing room is for the players - and the players only.
OK, so I never had a transfer in my career, but I used to love deadline day: Dimitar Berbatov turning up at Manchester airport with hours to go, Robinho coming to Manchester City instead of Chelsea.
Saturday afternoon is the hardest thing. I can go out and watch games, but I'm constantly on my phone looking at results: what score is this, what score is that. You have no real involvement, but you're obsessed with it.
United's history was built on attacking football, which does not always mean that the team kept clean sheets or did not concede chances.
If you go down the leagues, you have to understand what level you're working with, and if you get frustrated, then it's not going to ever happen for you. That's why a lot of managers don't succeed where they should do.
It is very difficult for me to breathe when it's hot and humid.
Things change, although I believe that certain principles - of attacking, entertaining football - should always be protected.
People say that Rooney could have been like Lionel Messi, a more prolific goalscorer who dribbles past opponents more. But they are different characters. You will never see Messi snapping around the heels of an opponent to win the ball back deep in his own half. Wayne does that all the time, and sometimes that enthusiasm will count against him.
My view is that the signing of players should be a simple process. The chief scout identifies them, the manager decides who he wants, and the chief executive is dispatched to do the deal. It really is as simple as that.
When I go into management, I want to do so with 100 per cent commitment.
I won three FA Cup finals, two League Cup finals, and played in one of United's two Champions League-winning finals. But I lost in a lot of finals, too: the FA Cup in 1995, 2005 and 2007, the League Cup in 2003, and the Champions League in 2009 and 2011.
As a player, I loved being tackled, whether it was in training or in a game. I took a full-blooded challenge as an invitation to do exactly the same thing to an opponent. I would wait for my opportunity and nine times out of 10, I would get him back.
The game changes so quickly, and you have to get yourself in a position mentally where you can deal with whatever is thrown at you.
As a finisher, there are few players as composed as Messi. When you can score as many different kinds of goal as he can, you have every reason to be confident.
Playing in attack is difficult. You are under scrutiny, and you have to be able to deal with that.
I was fortunate to play with so many wonderful footballers and under the greatest manager of all time, but I do believe that a club's ethos, the principles of how it plays, should outlive even the biggest individuals in its history.
At United, we never used to change our style much away from home. The aim was always to score goals and dominate the match.
In my world, the dressing room was sacrosanct. The only time anyone was permitted to take pictures in there was when we had won a trophy.
I expect positive play from Manchester United all the time, whether you're at home or away.
I was lucky enough to play at Old Trafford, and we always talked about the atmosphere on a Tuesday night, the special atmosphere you create, and the crowd is rocking when you go out for a warm-up.
In the periods of my career when I stopped passing the ball forward or when I stopped looking for the risky pass that might open up a defence, the consequences were the same. The manager stopped picking me. I got back into the team when I went back to doing it the way he wanted.
It's the thing I miss about football, I suppose: being with the team day-in day-out, getting a team ready for a Saturday afternoon, or getting yourself ready for a Saturday afternoon - it's the most difficult part.
You buy the right players for the system that you believe will be successful.
I knew the shirt-swapping business in general was getting out of hand when opponents would ask me for my shirt while we were still mid-match. Those are the wrong priorities.
I first remember Wayne Rooney from a game at Old Trafford in 2002 when he came on as a late substitute for Everton and, in a brilliant 15-minute performance, skipped past me on a couple of occasions.
When it came to playing Arsenal over the last eight years of my career at United, we always went into games against them feeling like we would win - and we usually did.
In some ways, I admire the principle of a manager who is determined that his team must play their own game.
There is something about a cup final that brings out a different quality in a footballer. Do they have the courage to win a one-off match?
It goes without saying that no one at United ever expected any help. We understood that decisions can go against you. We believed we were the better team, and therefore, if the referee got his decisions right, then we would win the vast majority of our games.
'Elusive' is the word that immediately springs to mind when I think about Messi's style of play. You think you have an eye on him and then - blink - he has gone, only to reappear somewhere else in space, with the ball.
Modern managers have a lot of demands on them, and many feel, with justification, that they do not have the time to commit to watching the junior sides.
What I like about Pochettino is the way that he looks in control. He is in control of his players, in control of the way that they play.
United fans don't care if the team only has 40 per cent possession as long as they are watching an attacking team. My experience was that the supporters understood that even our best teams, even the teams with Peter Schmeichel or Edwin van der Sar in goal, were going to concede goals.
When you are playing for a top club, when the pressure is on, when scrutiny is everywhere, you need some privacy. You need a place away from public view where people can be open, and, at times, difficult conversations need to be had.
I don't go looking for the post-match team pictures posted by players on Instagram, but usually, someone ends up showing them to me, or I notice them when they get printed in the newspapers.
To go and watch Manchester United, whether it's home or away, is entertainment; it's goals - whether you concede goals or whether you can score goals.
To beat opposing teams, you have to attack, and to attack, you have to take risks.
Part of being a Manchester United player under Sir Alex Ferguson, perhaps the most important part of being one of United's attacking players was that when you were in possession, you had to take risks in order to create goal-scoring chances. It was not an option; it was an obligation.
The hardest thing to coach is scoring goals and creativity.
Managers live and die by their recruitment.
