Andre Agassi says it. Tim Henman says it. Every leading tennis player knows it. Looking after No 1 is the only way to stay healthy.
Roger Federer looked after No 1 last week and missed the Madrid Masters, one of the nine major events on the ATP Tour. Having already qualified for next month's Masters Cup in Houston, and being guaranteed to finish the year as world No 1 after winning three of the four Grand Slam singles titles, Federer sent his apologies to Madrid and explained that he needed to rest his mind and body between engagements before competing in Basle this week.
He hopes to win his 13th final in a row and his first title in his home town tournament, where he used to be a ballboy. He also has a commitment to his Swiss sponsors.
Ion Tiriac, who owns the Madrid tournament, was not impressed, particularly since he had already lost the three players ranked immediately below Federer in the rankings, Andy Roddick, Lleyton Hewitt and Guillermo Coria.
"I appreciate the honesty of Federer, who, as a shot-maker, is the best player I ever saw in my life," said Tiriac, who has been the manager of Ilie Nastase, Guillermo Vilas, Boris Becker and Goran Ivanisevic. "He says, 'I am tired'. Why is he tired? He should not play so much before a tournament like Madrid. And now he plays in Basle. That is his home. He should play. But something is wrong.
"[Michael] Schumacher didn't stop after six races when he was world F1 champion. I think a tennis player who makes five, six, seven, eight, 10 million dollars a year should have the decency to make his programme and give back something to the game."
Tiriac advocates that any player who does not fulfil his Masters Series commitments should not be allowed to play in the Masters Cup. But he cannot imagine the ATP, who run the men's tour, taking such strong measures.
"Unfortunately, I don't believe they are going to do the surgery. They might do an aspirin here, an aspirin there to change it."
The 23-year-old Federer has reached the point where he cannot please everybody. Missing the Madrid tournament may be only the start of his readjustments to alleviate the demands on his time, on and off the court. The tennis calendar is suffocating, and, in spite of endless talk of change, there are few signs that the sport's various governing bodies are ready to alter the schedule and do some serious pruning.
Federer, in common with the most successful players of the open era before him - Jimmy Connors, Bjorn Borg, John McEnroe, Ivan Lendl, Boris Becker, Stefan Edberg, Pete Sampras, Agassi - will plan his year in order to peak at the four Grand Slam championships. To mark his triumphs this year at the Australian Open, Wimbledon and the US Open, Federer's shirt, shorts, headband and racket have been put on display at the International Tennis Hall of Fame in Newport, Rhode Island.
On this site after the US Open, Nick Bollettieri, Agassi's former coach, hailed Federer as the greatest talent tennis has seen. And yet, before he won Wimbledon last year, some observers questioned whether he had the nerve to win a Grand Slam title.
"Things have changed a little bit over a year," Federer says. "After the  French Open, where I lost in the first round, I was sitting in the press room trying to explain why and telling people to relax a little bit, and trying not to put too much pressure on myself. Here we are, six Grand Slams later, I have four of them, plus the Masters Cup, and in other Masters Series events I have four titles. Now suddenly I will be the greatest player ever. It's quite a contrast.
"In the beginning of my pro career, I didn't play so well in the finals. I always had the feeling that the other guys were playing unbelievably, and I could not do much about it. Suddenly, I started winning and turning the tide."
Numbers, however, tell only a fraction of the story. It is not only what Federer does, but also the way that he does it. He was first attracted to football before finding his niche in tennis, so it should come as no surprise that the 23-year-old Swiss admires the consummate skills of Real Madrid's French genius, Zinedine Zidane. Watching Federer play tennis can be like watching a swan glide serenely over water - it is easy to forget how much hectic activity may be taking place beneath the surface. So does the apparent ease of Federer's expertise in an individual sport demanding mental and physical strength and the stamina to cope with almost constant intercontinental travel and training for tournaments hide inner stress?
"I am actually quite calm inside, I have to say. Once I feel good on the court, when I'm sure about what's going on, I don't think about going crazy any more - losing my mind doesn't even come into my mind. The way I am on the court is also the way I feel inside, usually. Obviously, sometimes in tough situations I put on a little bit of a poker face. I cannot start having wobbly legs at break point. You have to get your act together."
How would he set his standard for being the best ever - by winning a certain number of Grand Slams, or by being No 1 for a number of years, or by playing at a consistently high level?
"I didn't say 'I want to be the best ever'. People are saying I have the chance to be. I'm conscious of that now, having won four slams at 23 years old. Hopefully, I'll stay healthy, so I can continue to compete, because this is what I love doing. If I break records, that's fantastic, but if it doesn't happen, that's OK."
Since winning his first Grand Slam title at Wimbledon last year, Federer has prospered without a coach. "I like to be in control of what's going on and I like to be independent," he says. "My parents and my coaches throughout my career have brought me up so that I can travel on my own. I felt like I needed that sense of self-reliance, because you never know what is going to happen."
Dynamic dozen: Federer's 12 successive final triumphs
Roger Federer - the winner of 21 singles titles - has triumphed in 12 consecutive finals, a feat matched only by Bjorn Borg and John McEnroe since tennis went open in 1968.
Federer's winning sequence:
Vienna October, beat Carlos Moya in final, 6-3, 6-3, 6-3.
The Masters Cup, Houston November, beat Andre Agassi in final, 6-3, 6-0, 6-4.
The Australian Open January, beat Marat Safin in final, 7-6, 6-4, 6-2.
Dubai March, beat Feliciano Lopez in final, 4-6, 6-1, 6-2.
The Indian Wells Masters March, beat Tim Henman in final, 6-3, 6-3.
The Hamburg Masters May, beat Guillermo Coria in final, 4-6, 6-4, 6-2, 6-3.
Halle June, beat Mardy Fish in final, 6-0, 6-3.
Wimbledon July, beat Andy Roddick in final, 4-6, 7-5, 7-6, 6-4.
Gstaad July, beat Igor Andreev in final, 6-2, 6-3, 5-7, 6-3.
The Canadian Masters July, beat Andy Roddick in final, 7-5, 6-3.
The US Open September, beat Lleyton Hewitt in final, 6-0, 7-6, 6-0.
Bangkok October, beat Andy Roddick in final, 6-4, 6-0.Reuse content