Be confident in what you do!

Just as the title says be confident in what you do! If it's a job or working out to going out on your first date. Hold your self up as if you already won/ are the best at what you do. Of course there is a limiting standard experience. But once you have that then stop doubting yourself or second guessing more then usual.

You were hired for a reason. Or the girl is dating you for a reason. Because YOU are good at what YOU do. So be confident and ALWAYS keep learning or staying ahead of the game. This will even solidify your confidence not only in your self but in other people also.

For weightlifters its almost a MUST to have a certain "swagger" about you. You don't walk up to the platform doubting your self scared that you can't make the next lift. Your looking down, demeaning the weight, making it do what YOU want to do. I even go as far as visualizing  me already completing the lift. Standing victorious as everyone else is cheering and congratulating me on how easy it was or how cool it looked.

If your confident enough and have the right tools and experience. You will perform to the best of you ability.