Perhaps the most revealing insight comes when Steven Gerrard is looking back over his England career and decides the best way to judge it is with a mark out of 10.
He wins his 100th cap in Sweden on Wednesday night, joining a distinguished club with only five other members, but there is a general rule in football: the most driven, successful players are never fully satisfied. Gerrard is a case in point. "Six or seven," he finally decides.
Not bad, is the underlying message. Not bad but, equally, not as good as he would have liked. And please, he says, don't refer to him as a "legend," either now or further down the line. Well, not unless England surprise everyone at the next World Cup and actually win the damn thing. "In football, the hero and legend status is given out far too easily for my liking," he explains. "As far as playing for England goes, there are only 11 real heroes over history. The rest haven't really delivered, for me."
Gerrard has always been a harsh self-critic and that is not about to change just because he is on the verge of joining Sir Bobby Charlton, Sir Bobby Moore, Billy Wright, David Beckham and Peter Shilton in the small and exclusive band of England centurions.
The truth, he says, is that his international career will always be laced with a certain amount of regret. How could it not be when he was part of the so-called golden generation, playing in the team that thrashed Germany 5-1 in Munich but that never got their act together in the tournaments and then disbanded? "We under-achieved," he is willing to admit. "That team should certainly have got to a semi-final. That group of players should have done better. That's certainly a regret now."
There have been other disappointments. Typically, Gerrard remembers the bad games just as vividly as the good ones. "It's three times for me," he points out when the conversation turns, as it always does, to England's anguish in penalty shoot-outs. "I don't think any other international player has experienced that." He is "a great believer that you learn more from the bad times".
England's game against Greece in 2001 is another one he picks out. "A bad memory," as he recalls it. Gerrard had been in trouble before that match for, as he puts it, "being out a bit late past bedtime". It was his first really disappointing performance in England's colours and it has stayed with him. "Beckham scored the 'worldy' free-kick, but that was a disappointing individual performance by me." The worst game, he says, of his 99 to date.
And yet, lest it be forgotten, we are talking about one of the modern greats, the player everyone else in the England dressing room looks up to and the obvious choice when Roy Hodgson took the manager's job and wanted a new captain. Gerrard still has the armband from when he first was given the honour. That, too, was against Sweden, in a 2004 friendly in Gothenburg.
The first cap came against Ukraine in 2000 when Gerrard was not quite the worldly, streetwise operator we see now. "I'd travelled down in the same car as Robbie Fowler and Steve McManaman," he recalls. "I'd told them how carefully I'd packed my bag. My mum had done my undies, ironed all my socks. I went back to my hotel room after training and everything was in the bath, with the water running." Gerrard had turned 20 the day before the match. "Happy birthday soft-arse" was written in foam on the mirrors.
By his own admission, the young Gerrard could be terribly anxious at times. At Euro 2000 he remembers the homesickness was so bad he rang his mum at one point and told her he wanted to come home. When England played Germany in Charleroi he was such a bag of nerves that an opponent, Dietmar Hamann, came over 10 minutes into the game to check on him. "Just do what you do for Liverpool," Hamann said. Gerrard can remember telling his Anfield team-mate: "I'm absolutely crapping myself here."
Yet Gerrard always had that competitive spirit to get him through. In that same match Hamann took the ball around him. That didn't happen often in Liverpool's training matches. Gerrard flattened him.
Consider, too, his story about his debut, as Tony Adams went round the dressing room bawling at players individually. "Are you ready?" Adams screamed (expletives removed) when he got round to the new boy. The truth was Gerrard had never seen anyone so worked up before a football match.
"Jesus, hellfire," he remembers thinking. Yet he returned the captain's gaze. "You bet I'm ready."
Twelve years on, Gerrard will wear special one-off boots with '100' sewn into the side in Stockholm. Yet conversely, the distinct impression is of someone not entirely comfortable with all the attention. It would be "disrespectful", he says, to compare himself to Charlton or Moore. Pressed further, he explains "they are 10s" in his marking system.
Yet there is enormous pride, too, about what he has achieved. "I'm not usually a player who shows his emotions but this is special for me. I don't think it will really sink in until I retire."
He had come close to doing just that at the end of Euro 2012. "When you are at my age and you have had another setback at England level it crosses your mind. I'm being honest and, yes, it's crossed my mind on a couple of occasions. It's just that being the captain and the buzz you get playing for England outweighs the thoughts about knocking it on the head."
The next World Cup will almost certainly be it, leaving Gerrard to concentrate on the final stages of his Liverpool career. After that, he will take his coaching badges. One day, he says, he is not against the idea of managing England. "We'll see where it goes. I have always said I will only be a coach or a manager if I feel I am good enough. But I don't think you go down that road just because you've been a decent player."
One certainty is that Gerrard will give it everything he has, just as he always has done. "I always go back to what my dad said to me when I was eight years old going to the Liverpool centre of excellence: 'You get out of football what you put in.' If you work hard and make the sacrifices and you are willing to learn and you have the talent — you'll have a good career.
"That's the advice I have always tried to stick to. I have always tried to give my best for England and every time I have played I have given it all I have got. I admit that my performances have never always been great but it has not been because of not wanting to be here, or lack of effort, or it not mattering to me as much as club football."
And tonight? How will he feel walking out for his 100th cap? "It's difficult to put into words. The hairs will be standing up on the back of my neck. It's a real honour, a privilege. When I'm an old man my family, my kids and their kids, will see my name on that list now. That's what I really like about it."
Gerrard on his...
"Zidane. Magical feet. Feet like hands. Special."
"Wayne Rooney? Paul Scholes? Probably Scholes, I would say. I appreciate what he has got. I like him as a person. What he's done at Manchester United, as well. To see him in training and play alongside him..."
"The 5-1 in Germany. Because of who it was against and how emphatic the result was. In their backyard. It's difficult to beat that. That was the strongest England team I've played in."
"I always go back to Greece when Beckham scored the worldy free-kick. That was a disappointing individual performance by me. That game was on the back of me being out a bit late past bedtime so that's a bad memory."
Best three goals
"1) I scored a volley against Macedonia at Southampton, that was a decent strike. 2) I ran past three men in the area and scored at Wembley against Hungary. 3) And the one against Germany (the 5-1): the pitch being wet helped that goal go in, if it had been dry it might not have gone in but they are the bits of luck you need to score good goals and win big games."