The psychological impact of self talk has been well documented.
When I was in college I took an entire course about sports psychology, and my biggest takeaway is that the inner dialogue you have with yourself has a major effect on your performance.
If you pump yourself up and tell yourself you will make the shot, you are more likely to make that shot. If you trash talk yourself, that negativity is going to impact your performance for the entire game. There is tremendous power in being positive, and not just in sports, any workout program or exercise regimen will benefit from positive self talk. Certified fitness experts tend to agree on this point, which is an idea as old as the book The Power of Positive Thinking. It all goes back to positive reinforcement, which is what we use to raise children and train animals, but you can use it on yourself in the context of sports or workout classes. Push yourself a little harder every time in the cross fit class, just because you believe you can do it. Push beyond what your personal trainer sets as a goal, just to show that you know you have it in you. Confidence is a muscle, and the more you work it, the stronger it gets, and the harder it works for you. You don’t have to play sports, you don’t even have to go the gym or work out at all, just be positive in whatever you do and grow that confidence! Believe in yourself, and know that you can achieve it!