Yes. Confidence is so important in today's society. I believe confidence starts on the inside, but continues to surface on the outside with regard to how we feel about the way we look. All other confidence though, comes from the inside. Examples of this include the confidence in our brain power and the confidence in our ability to succeed.
Try saying a bunch of confident things in your head all you want but if doing so doesn't lead to any changes in your body language or facial expressions or how you talk or communicate in general in order to make it look more confident as is constructed by others and then you will not reap any of the benefits of appearing confident in social situations.
Same with activities like sports. You can tell yourself you believe in yourself and that you can do it all you want but unless that in turn stimulates you to alter your behavior to be more focused on the task at hand it isn't going to do sh!T for you.
Personally, I believe in doing tasks in the most efficient way that I know regardless of whether I think it will end in success. Then whether I am confident or not doesn't matter. I used to think that it did and that confused me when I was a kid and I told myself to be confident and not only did it not work but people around me continued lecturing me and telling me I seemed unconfident.
If you want to succeed in live focus on behavior and its reception by your audience and how it physically effects the environment, not some mystical 'inner world'.