They never come back. It’s one of the most ancient principles in sport. And yet Justine Henin, the wonderful Belgian tennis player, has announced that she is making a comeback, further spicing up the already sizzling women’s tour. Henin, with her miraculous timing and her glorious one-handed backhand, will be welcomed back by everyone in sport.

She follows hard on the return of her great rival, the equally Belgian (and equally famous) Kim Clijsters, who won the US Open a couple of weeks back as a wild card. Her gymnastic style and incongruously sunny disposition had been greatly missed, but after all but two years away and now a mother, she is as good as she ever was.

I’d be surprised if Henin wasn’t able to reach her own former levels of excellence — because that thing about not coming back is just not true. Not, at least, if you happen to be a woman. As a general rule, it’s true that men don’t come back: John McEnroe took a year’s sabbatical and was never the same. Muhammad Ali is one of the very few great athletes who made a successful comeback — so much so that he kept doing it, to his ultimate and desperate cost.

But women do come back. Sport is full of women who have made successful comebacks. Often enough, it is a return after motherhood. Evonne Goolagong Cawley came back to win Wimbledon as a mother, and Lindsay Davenport also came back after giving birth.

But that’s not always the case: Jennifer Capriati came back after personal trauma. She cracked after years as a bullied wunderkind and had a brief period as a bad teenager. But then she regrouped and decided to go back to tennis on her own terms. This is also a regularly repeated pattern. Some brilliantly talented young female athletes operate in an intense and oppressive relationship with a coach or parent. They become women and wish for a change. And they decide to go back to what they are best at — but this time for themselves.

This sort of thing has happened many times in swimming. Sharron Davies, who these days presents swimming for the BBC, retired in 1980 after winning a silver medal at the Olympic Games of that year.

She came back in 1989 and won two bronze medals at the Commonwealth Games of 1990. Alyson Jones won a bronze in the Commonwealth Games of 1974, then left the sport to study medicine. In 1985, Dr Jones rejoined the Great Britain team.

In athletics, Paula Radcliffe stepped out of the sport to have a baby, and returned to her city marathon-winning best. Mary King, the eventer, has had two children, and so came back twice.

She is still at the top of her sport and only missed making the Britain team for the European Championships this weekend because her top horse is injured.

Perhaps my favourite example is Fu Mingxia, the Chinese diver. She was the little waif of the Barcelona Olympics in 1992, winning gold at the age of 13 and unforgettably being photographed against the great cityscape behind the open-air pool. She won gold again four years later in Atlanta and then retired. She went to college and lost condition — so much so that people asked in wonder: “Were you really an Olympic athlete?”

Incensed, she got back into training and won gold in Sydney in 2000. At the first two Games, she competed because she was told to. In Sydney, she did it for herself.

You can, if you wish, move into areas of thrillingly dangerous speculation here. Why should this be? Is it because women are softer than men? Or is it — as anyone who has given birth will tell you — because women are basically a good deal tougher?

Germany out on penalties – jump for joy when we can

How extraordinary sport is. Just when you get a little weary of the easy predictability of it all, sport starts throwing up ludicrous results. Chelsea — more or less out of the blue — got hammered away to Wigan Athletic on Saturday. The England one-day cricket team, who had been playing like the most dismal bunch of losers in the never-ending post-Ashes series against Australia, suddenly started playing like giants and beat the glorious mavericks of Sri Lanka entirely on merit.

And here I am in Fontainebleau for the European Eventing Championships wondering what on earth happened to the Germany team. They came here as hot favourites and their first rider, Michael Jung, set the tone with a magnificent clear round inside the time. But then things began to go most terribly wrong and self-doubt and failure ran through the team like a virus. One after another, the Germans acquired jumping penalties and time penalties and then elimination, some by falling, some by stopping, some by refusing.

It was an extraordinary procession of disaster, each error leading with dreadful inevitability to the next. Of course, one has every sympathy with the people and the horses involved, but it is hard to find complete detachment when the Germans lose on penalties.

Kieren Fallon packed a punch from the start

Kieren Fallon is making a comeback. But this wasn’t a retirement that went wrong: rather, it was an 18-month suspension for cocaine. Fallon is a brilliant jockey, a disaster-prone human being, and not a man whose toughness has ever been in serious doubt. He is the subject of an excellent biography by Andrew Longmore. As ever in such works, it is the stuff at the beginning that intrigues most, just where and how the exceptional nature of a person makes itself plain against an unexceptional background.

Fallon was boxing for Connacht’s under-13s against Munster’s under-13s. His opponent was older, bigger, more experienced. Jim Regan, the Munster coach, said that he would pull Fallon out if things got too rough. Fallon said: “He’s only got two hands, same as me.” Regan told Longmore: “But, you know, Kieren pulled the house down that night. The other fella came out like a tornado, throwing punches from everywhere, and Kieren came back to his stool at the end of the first round and said he’d never felt a thing.

“Kieren knocked him out in the third round.”

Fixers are the real culprits

Professional sport can only exist as a matter of trust. If you can’t believe that both teams, that every individual really, really wants to win, then the entire exercise has no point. The bubble bursts. It becomes a grotesque and meaningless ritual.

And that is why match-fixing is such a terrible thing in sport, and why the suggestion that results have been fixed in obscure Champions League matches is, in sporting terms, so disturbing. Sure, there are many worse things you can do as a human being in sport — like, for example, telling your driver to crash his car — but cheating is an aspect of sport, one we know about, understand and try to deal with.

But the fixing of a result is a denial of sport. Fixing destroys that element of trust. And when trust goes, sport has no reason for existence.