Theo Walcott is not going to get ahead of himself. He's going to take each match as it comes. Good plan: taking matches in batches never works out well. He's calm, he's modest, he's level-headed and he's the best young player since Pelé. Isn't he?

Oh, I've seen a thousand Pelés in every sport I have watched. Mark my words, one day this boy will play for England. This one has the potential to go all the way. He's got the lot, yes, and a fine, solid family background. And the frightening thing is this: he can only get better.

I remember the best English centre forward I have seen, leading Nottingham Forest to a five-goal rout. Brilliantly two-footed, shark-like in the way he hunted down centre backs, omni-directional vision in the way he created goals, utterly remorseless in the way he helped himself. Not even a World Cup victory was out of the question with Stan Collymore leading the line.

Well, not for the first nor for the last time, I was a fraction out with my predictions. Collymore lacked the talent for having talent and, alas, his mental frailties overcame him. He was one of those that got away. So it goes.

But we can't help rejoicing at mere possibility. It's a joyous thing to see a young player emerge in any sport, fresh, naive, unafraid, amazed yet unfazed by his brilliance, leaping before us like Blake's Glad Day: a new hope, a new dawn for humankind. Walcott was like that on Wednesday evening as he scored his hat-trick for England against Croatia. We haven't experienced such hope in the England football team for, oh, as much as four years.

Wayne Rooney exploded into our consciousness at the European Championship of 2004, galvanising all around him with his impetuosity, his power, his control, his vision, his glorious belief that he could beat anybody you cared to put in front of him.

That tournament turned when he got “metatarsaled” in the quarter-final against Portugal, but no matter, a star was born and England were going to march on and win the World Cup in 2006. The head coach at the time, Sven-Göran Eriksson, built his team wisely around Rooney and we were all set for fireworks. Then a couple of weeks before the finals began, Rooney got metatarsaled again, the plan was in disarray. Plan B was to wait until Rooney got fit again. He tried all right; he failed. So it goes.

I remember when Graeme Hick was the greatest talent cricket had seen and was about to lead England into a period of dominance. Alas, Hick's natural diffidence and his rigidity of technique meant that he was never a great player at international level.

You don't know. You can't know. You can only hope. I can recall all the sentimental hard-nuts among the sportswriting profession (the dominant type, it must be said) who maundered on about the beauty and perfection of Amir Khan at the Athens Olympics of 2004. Four years on, Khan has been exploded, just another Icarus who flew too near the sun. So it goes.

So let me tell you about a tennis player who was despised for his failing of nerve when he was 19. He won a grand-slam tournament at this precocious age and was once overwhelmed by his own achievement, talking about the responsibility of being a champion, at the relief when he lost his title the next year.

He was despised among many commentators (sentimental hard-nuts) for not being the stuff of which champions are made. His name was, of course, Pete Sampras, still, in terms of grand-slam tournaments won, the greatest tennis player that ever picked up a racket. So it goes.

It becomes clear, then, that the real problem of promising young athletes is not the capricious nature of youthful talent, but the flawed way in which we make our judgments.

Andy Murray has for some years been the great hope of British tennis. Then he became a petulant poser who would never cut it at the highest level. Now he has a grand-slam final on his CV.

Some see him as a certain future champion, others as a long-term disappointment. What's more, opinions will change with every big tournament he plays. Me, I see a player on the upswing who has already reached a final, but I have no idea if he can take the next step. I hope so, I even feel I think so. But I don't know so. I can't.

Much of sport, like much of life, is repeating, going round on a loop like Finnegans Wake: promise, achievement, fall; and even more often, promise and fall without the achievement in between. Perhaps we should learn some perspective, some sense of proportion.

Turtles and the sea, turtles and the sea. That's the way it is with sporting promise: thousands of young and hopeful athletes moving towards the oceans of fulfilment and achievement, while all around them, the gulls of failure gorge themselves as the fish of disappointment wait a few yards offshore.

How many turtles make it to adulthood? How many get to father or to mother little turtles? Very few; just enough to keep the whole thing moving and working and marching on.

Charles Darwin had his eureka moment, not on the Galapagos Islands but when reading Malthus years later. Then the realisation hit him: more are born than can survive. This prompted the great question: why do the diers die and the survivors survive?

And, at a stroke, the way we understand the world was changed for ever and the theory of evolution by means of natural selection was established. Many young athletes crawl towards the deep oceans of sporting success.

Why do some succeed and many fail? Why do some of the most promising fail at the moment when all is before them, while others, less eye-catching, doggedly flipper themselves onwards towards

ultimate success? It is a mystery as deep as the one Darwin was plumbing.

So we should be wise about Walcott and say, well, perhaps we have already seen the best of him and that we should be thankful for what we have already received. And you are perfectly welcome to do that if you wish. Me, I prefer to take another direction.

Naivety in short supply is destructive of the sporting experience. It is impossible to enjoy sport without a naive, even an utterly unrealistic, understanding of what you are watching. You have to think that sport matters, for a start, which is a ludicrous proposition from any grown-up point of view.

So, more or less as an effort of will, I will retain the hope that Walcott will become a wonderful player for England, who will ignite England at the World Cup in South Africa in two years' time, and will continue to do so over the next dozen years. I may have my fair and just and logical and reasonable reservations about the likelihood of all this, but I'm not listening to them. Instead, I'm wishing him an ocean of luck.