This story is part of Peak, The Athletic’s desk covering the mental side of sports. Sign up for Peak’s newsletter here.Dale Earnhardt Jr. won 26 races in his career and was inducted into the NASCAR Hall of Fame in 2021. He is a race analyst for TNT.If I could go back and talk to myself, if I could go back and re-run my career, there’s one thing I would work on the most: My confidence during races.It’s the biggest challenge in racing, and I think it gets overlooked. People talk about reaction times or having a great rapport with your crew chief. But if you don’t have the mental toughness to stay confident in a race, you don’t have a chance.I went into most races believing that I was the best. Remember, I was racing against guys like Jimmie Johnson, Jeff Gordon, Tony Stewart. I know those guys believed they were the best, too, and there’s a great argument that Jimmie is a much better driver than I was. I wouldn’t fight that argument at all. But I had to believe I was better or I was wasting my dang time.During a race, though, it’s really, really hard to maintain that unwavering confidence. Actually, I think it’s the toughest thing in racing.When you’re driving a race car, you basically partner with your car. The problem is you’re not sure on any given day what the car is capable of.If you’re a runner, for example, you know your body. You know what you can do. You know what your body feels like that morning. You can probably guess what kind of performance you’re going to put in.As a driver, you know how smart you think you are. You know how talented you think you are. You know that given the right machine, you can do all the right things. But every day the machine is different. Every day the tires are different. Every day the setup on the car is different.Every race you’re going to drive down into the corner for the first time unsure of the kind of partner you have that day. It’s hard to remain positive in a tough, uncomfortable environment. It’s 130 degrees. You’ve got three-and-a-half or four hours of racing. You’re busting your ass.