In a 2010 interview with Interview Magazine, Jay-Z revealed that in 2003, Eminem wore a bulletproof vest to the studio when he collaborated with Jay-Z on ‘Moment of Clarity', which he produced on The Black Album.
“I never even told him this, but I remember that Eminem came into the studio when we made ‘Moment of Clarity,' which he produced, on The Black Album. So here's Eminem. It's 2003, I think The Eminem Show had come out, and he was, like, the biggest rapper in the world —he sold, like, 20 million records worldwide or some ridiculous number. Jay-Z told Interview Magazine
“But when he came to the studio, I remember I hugged him and I could feel that he had on a bulletproof vest. I couldn't imagine being that successful. I mean, he's a guy who loves rap and wanted to be successful his whole career. Then he finally gets it, and there's this dark cloud over him. There's this big beef between 50 Cent and Ja Rule and between real people, too—so he has to worry about that. He has to be afraid to walk around New York freely. I was like, ‘Here it is. You've gotten everything you wanted, and now you're a prisoner of your own fame.' That's sad to me that you have to walk around in a bulletproof vest after you've sold 20 million records. So, the point being, what I'm interested in is the thing under the thing. You can think you know where he was at when he said those raps, but I saw another level of it personally, and I found it sad.” Jay-Z added.