Ahead of his matches at the U.S. Open, Novak Djokovic—winner of 16 Grand Slam singles titles and ranked No. 1 in the world in men’s singles tennis—spent some time in New York promoting a collaboration with luxury pen company Montblanc.

Sales of the limited-edition StarWalker Metal Fineliner pen and matching notebook ($740) will help raise money for the Novak Djokovic Foundation, which supports preschool education in his native Serbia.

At a private event in Manhattan’s Meatpacking District, Djokovic talked to Montblanc customers and dealers about his writing habits, and then sat down with Bloomberg to discuss them further. Unsurprisingly, Djokovic says his preferred writing instrument is a Montblanc, though if he needs to get a thought down, any cheap pen will do.

You mentioned that you journal every day, or almost every day?
Not every day, but I guess when I feel inspired, I usually write about ideas that come to mind and things that make me feel good, positive, joyful. But I was mentioning that the biggest quest and challenge for me is to write when I’m not feeling at my best, and when I have experienced something that has triggered some emotions that are not so positive.

And that’s usually when the journaling has the most effect. Because that’s when you dig deep, and that’s when you really—by writing—you’re sharing the emotions that bother you, that make you feel alone.

Journaling has been part of my career for a long time. Ever since I was seven or eight years old, I have been writing things down—how I feel. At the time, it was the most basic things, related to tennis mostly. I was taught to journal by my tennis mother, as I like to call her, a lady who was my first coach ever and conveyed a big passion for the sport of tennis to me.

Do you have a go-to notebook, or do you use whatever you have handy?
It’s a combination of both. I do have the notebooks, mostly at home, and I do take them, but sometimes I just feel like writing on whatever is handy. So sometimes in the hotel room, I find a little pen and paper they have next to the bedside, and that’s where I write things down. Because usually just before you go to sleep or just when you wake up, you somehow get mostly inspired to write and to share something.

So even a hotel pen is fine, a Bic?
If it’s an emergency case, I guess, but I try to have my Montblanc pen always with me. So usually, if I write in a hotel, I would have my notebook and Montblanc writing instrument bedside, so then I would use that.

You use a rollerball , a StarWalker rollerball?
Yes, exactly. I like the pens that are very light in my hand and that glide and slide through the paper easily. Sometimes, I want to write a few phrases and not really go deep, and sometimes … it might sound funny, but sometimes when I was writing for a longer periods of time, and I wouldn’t have a lighter pen, I would start to feel uncomfortable with my right wrist. So that’s also quite important for a tennis player.

This article was provided by Bloomberg News.