The Australian Open took me to a place that had never been a part of me before—to an extreme confidence that some people call being “in the zone.” I really can’t explain it—but it was a good place to be.

The clay at the French Open exposed virtually all my weaknesses—for starters, my inability to slide on it—and forced me to overcome them. Twice. That felt good.

These courts revealed my true essence. Behind the photo shoots and the pretty tennis dresses, they exposed my imperfections—every wrinkle, every drop of sweat. They tested my character, my will, my ability to channel my raw emotions into a place where they worked for me instead of against me. Between their lines, my vulnerabilities felt safe. How lucky am I to have found a kind of ground on which I felt so exposed and yet so comfortable?

One of the keys to my success was that I never looked back and I never looked forward. I believed that if I kept grinding and grinding, I could push myself to an incredible place. But there is no mastering tennis—you must simply keep heeding the demands of the court while trying to quiet those incessant thoughts in the back of your mind:

Did you do enough—and more—to prepare for your next opponent?

You’ve taken a few days off—your body’s losing that edge.

That extra slice of pizza? Better make up for it with a great morning session.

Listening to this voice so intimately, anticipating its every ebb and flow, is also how I accepted those final signals when they came.

One of them came last August at the U.S. Open. Behind closed doors, thirty minutes before taking the court, I had a procedure to numb my shoulder to get through the match. Shoulder injuries are nothing new for me—over time my tendons have frayed like a string. I’ve had multiple surgeries—once in 2008; another procedure last year—and spent countless months in physical therapy. Just stepping onto the court that day felt like a final victory, when of course it should have been merely the first step toward victory. I share this not to garner pity, but to paint my new reality: My body had become a distraction.

Throughout my career, Is it worth it? was never even a question—in the end, it always was. My mental fortitude has always been my strongest weapon. Even if my opponent was physically stronger, more confident—even just plain better—I could, and did, persevere.

I’ve never really felt compelled to speak about work, or effort, or grit—every athlete understands the unspoken sacrifices they must make to succeed. But as I embark on my next chapter, I want anyone who dreams of excelling in anything to know that doubt and judgment are inevitable: You will fail hundreds of times, and the world will watch you. Accept it. Trust yourself. I promise that you will prevail.

In giving my life to tennis, tennis gave me a life. I’ll miss it everyday. I’ll miss the training and my daily routine: Waking up at dawn, lacing my left shoe before my right, and closing the court’s gate before I hit my first ball of the day. I’ll miss my team, my coaches. I’ll miss the moments sitting with my father on the practice court bench. The handshakes—win or lose—and the athletes, whether they knew it or not, who pushed me to be my best.

Looking back now, I realize that tennis has been my mountain. My path has been filled with valleys and detours, but the views from its peak were incredible. After 28 years and five Grand Slam titles, though, I’m ready to scale another mountain—to compete on a different type of terrain.