It has been more than three years since Chris Evert wrote that controversial open letter to Serena Williams in Tennis Magazine.

Outlining Serena's amazing capabilities and strengths as a player, which we all know far outweigh her few weaknesses, Evert made the case that Serena should return full-time to tennis, lest she look back on those missed years with great regret.

According to Evert, Serena’s peak years were flying past her and she made the case that a player of such extraordinary talent and skill should be winning at least two Grand Slams a year. Talk about pressure.

Serena has never responded directly to Evert, but in some ways Venus sure has. "We love this sport and we dedicate everything that we have. But we just have other interests as well and we feel we should be able to explore those as well," Venus said at the 2007 US Open.

Serena has admitted: “When you travel to the same cities year in and year out, and eat the same foods and go to the same places and play against the same people ... things can get boring. It's important for us to keep our love of tennis alive. Our path is just different."

It seems that the sisters have indeed thought this over quite a bit. But what does their position say with regard to their involvement in the sport and the history that they make every single time they step on to a tennis court?

"The Williams Sisters should have at least 13-15 Slams a-piece," Matt Cronin of Fox Sports declares. And he is not the only one who feels this way. Many tennis fans and commentators alike feel cheated by the sisters and their non-tennis affiliated extra-curricular activities. With their astonishing power, fierce athleticism and now their refined shot-making, the Williams sisters have bested the rest of the women's field several hundred times over.

Between them, they have won every single major, Olympic, tier 1 and tier 2 title that there is to take. What else is there for them to do? According to Evert, and many more, it's about adding up the Slam count. But, as we've seen from athletes, there's a big difference between what the public wants from them and what they desire for themselves.

Michael Jordan retired at the height of his basketball career due to the sudden and tragic death of his father. The Williams sisters also suffered a tragedy, with the death of their oldest sister Yetunde. Both incidences sidelined history-making careers and caused the athletes to re-evaluate what's important to them.

Obviously, to the Williams sisters, it's not winning more Slams than Evert or Margaret Court. They appear to aspire to their own greatness. "I'd love more Slams, sure,” Serena said after her 2008 Wimbledon final loss to Venus. “That's why I play. But I'm not beating myself up for not winning more. I play to win. And I've learned to live and be happy even if I don't win a Slam that I want really badly.”

The sudden retirement of Kim Clijsters and Justine Henin, among other top players, also adds to this question. Henin and Clijsters did exactly what pundits, fans and commentators wanted. They played every tournament, Slam and Olympics possible. Then, out of nowhere, when they became exhausted, they both retired at the peak of their careers ... permanently. As they both put it, they accomplished what they wanted to do and they were burnt out. They were tired of playing tennis full time and they wanted to live their lives and do other things.

Hmmm. Isn't that all the Williams sisters wanted to do all along? Play tennis yet have other interests? I don't fault Henin and Clijsters for leaving tennis. They both accomplished great things and are dearly missed. However, I believe they both act as a great warning for the tennis world.

Tennis is a year-round sport with an extremely full calendar. Player burn-out is inevitable if these athletes do not take some time away for themselves. The Williams sisters did this before we saw the results of blatant over-playing and over-work of tennis athletes. The sisters made the decision to take time away and chase other dreams and thus be refuelled to come back on tour and try to win more titles and make more history.

Now they're both so well-rounded and satisfied with all their accomplishments – both on and off the court – that they've decided to play for at least another five or six years.

Even if they were to never win another Slam or major title (though Venus wins Wimbledon as though she was born treading grass and Serena guts herself through one major title after another) they'll still be around. They will still be playing. They will still be making history. And if that isn't commitment to tennis, then I don't know what is.

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