I have always had the overriding feeling that I am not free to set my own course. Stanley Milgram, a Harvard psychologist, felt the same. He conducted experiments in which people believed they were inflicting lethal electric shocks on others. Milgram proved that many people are prepared to kill if they are absolved of the responsibility.

That's how I find playing football under some managers and certainly how I see some other players. "The gaffer's son", which is how these players are known, will carry out any instruction that his manager gives him (especially if it involves cutting a fellow professional in half), not because he is an arse-kisser but because it is how he is programmed. Mentally, he is at his happiest when he is carrying out somebody else's instructions.

The psychological side of the game comes to the fore at a time like this, when the run-in to the season is firmly upon us, meaning that the mind games have gone into overdrive. Sir Alex Ferguson is the undoubted master of this art and has a long list of victims, most notoriously Kevin Keegan.

On the other side of Manchester the queue for the psychologist's office must be out the door. A couple of weeks ago, Roberto Mancini said on the back of a defeat at Arsenal: "While you still have a chance, you should do everything and we have six games so never say never." Fast forward a week and after a convincing win against Norwich, the Manchester City manager said: "The title race is still over. Against a strong United side, it is impossible for us to win this title from the position we're in."

Ordinarily I'd say players pay little attention to a lot of what their manager says to the media but at this level, and with the spotlight Ferguson and Mancini are under as their two clubs go head to head for the title, it will have been impossible for any of them – even Mario Balotelli – to ignore each manager's attempts to unsettle the other.

And while there isn't anything out of the ordinary where Ferguson is concerned, the self-deprecating tone of Mancini's comments and the fact that nobody seems able to work out where he is coming from, including possibly the Italian himself, must be a source of confusion in the City dressing room. An alternative view would be that it has had the desired effect on the United players, given their recent wobble.

I have been party to all kinds of mind games in my career but the one that still grates with me is the occasion our manager stuck pages of derogatory comments attributed to a rival manager on the dressing room wall prior to the match against his team. After we'd won, he told us they were fakes. I didn't like that at all and neither did the other players.

On the pitch, mental toughness is a most important attribute. The crowd are trying to get to you, the other team are winding you up, when you make a mistake your own players and bench get on your case and sometimes it feels like even the officials are conspiring against you. Mentally weak players are the ones that make excuses in this situation. Nothing annoys me more than when a player having a bad game throws his arms around and screams at people in an attempt to convince the crowd that it is the fault of the guy he was trying to pass to. I've lost count of the amount of confrontations I've had at half-time with players that put on this cowardly act. I put them in the same category as the ones that run off in the opposite direction to celebrate tapping home from two yards after the winger has beat three men and put it on a plate for them.

The truth is that I'm not overly tough upstairs any more. As time has gone on my capacity for mental fortitude has become severely reduced through a combination of struggling with authority (which has always been a problem for me, as regular readers of this column will by now have realised), becoming a senior professional, money, honours and a track record that reads as it should.

But what I have come to realise is that it's amazing how much the mental side of the game complements your ability with the ball. You can have all the skill in the world but if you lack that bit of steel and drive to continue doing what made you successful, then you won't get very far. And right now, I'm not getting very far.

The same can't be said for the United and City players who will have the title in their sights on a night when the result may well depend on an individual who mentally switches off at the wrong moment. It could come down to following the ball rather than the man when Agüero and Silva play a one‑two around the box, or remembering that Valencia always has a touch inside before he goes outside (like Giggs used to), or not forgetting that the midfield very often pass Rooney on when he enters the penalty area only for him to score a header between two giant centre-halves who think he is being tracked.

Maybe it will be the moment Kompany dives in when he should stand up on the edge of the area or perhaps it will come down to remembering that Rafael goes walkabout with the ball and leaves gaping holes down the right flank when he is dispossessed in the middle of the pitch. It may be "roughing up" De Gea at the right moment or winding up Balotelli when he has just missed a chance. Staying alert to all these opportunities when they present themselves could be the difference between winning and losing at the Etihad Stadium.

As for Milgram's experiment, Peter Gabriel wrote a song about it which features on his album So. The song includes the repetitive chant "we do what we're told". During the darkest days of my depression I listened to this song over and over, day in, day out. I have no idea why and, to be honest, it makes my head hurt just thinking about it.

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