Assessing the 33-year-old phenomenon that is Serena Williams has taken an interesting twist.

In an ESPNW article exploring the 20-time Grand Slam winner's ability to come back in matches - that was on display over and over at last month's French Open, a mental game coach claims that getting behind in matches works to Williams' advantage.

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"Patrick Cohn, a mental game coach and owner of Florida-based Peak Performance Sports, said that for Williams, falling behind in matches may have a subconscious benefit: helping her conserve emotional and physical energy. Over the course of a tournament, that helps her."

It's a plausible explanation, only because of Williams' uncanny ability to ramp up her performance when she needs it the most.

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"So I think sometimes [Serena] comes out flat," 18-time Grand Slam champion Chris Evert told ESPNW. Sometimes she comes out maybe not 100 percent fully engaged, like she kind of cruises along and then maybe it hits her, her pride [telling her], 'I don't want to lose this match' ... and she'll start slapping some winners and she'll give you that scream and then she's won the match."

It's that belief that Williams doesn't always have that killer instinct that might be a factor in her likability. The Washington Post reported that Williams, who is halfway to the calendar Grand Slam, says she's not even thinking about how such a feat might affect her legacy.

"I don't know how this sounds, but it's not on top of my list," she said, still sniffling from the flu-like illness that nearly derailed her run in Paris, the Post reported. "My list right now is to do well at Wimbledon. And then my list is to do well at the U.S. Open. And then Australia."

In fact, the Post reports, she's not even concerned about what might happen to her legacy if she fails to win another major.

"I don't really think, nor am I overly concerned, about winning a Grand Slam at this stage of my career. I think five years ago - yeah. Ten years ago, yeah it might have. Now I've got enough. I don't need a Grand Slam to define my career whereas maybe a few years ago if I didn't have 20 Grand Slams then I would have needed that."

Still, Evert marvels at Williams' ability to achieve a level of intensity that allows her to continue to win slams.

"I know this from my own experience," she said. "My last US Open I played probably one of the best tennis matches in my life beating Monica Seles. ... And then in the next round, I lost to Zina Garrison, who I owned. I never lost to Zina Garrison. I was flat."

So it may be that Williams simply has mastered the art of being flat.