When we look in the mirror, the light reflects back to show us an image of ourselves.
The physical properties of the light and the resultant image are predictable. However, what we see in our mind completely depends on what we were looking for in the first place.
If you see a happy, confident, beautiful person then that is the image you already had of yourself before you looked into the mirror. Quite often we don't see the good things, though. We find the flaws and we focus intensely on those.
Train yourself to look for the good first.
There is plenty to see that is good, not only in ourselves, but in everyone around us. But, we should look for it first. It's easy to pick ourselves, or someone else, apart when we look only for the flaws. If this is our natural process, though, we create negative feedback loops in our brains that reinforce the bad. Those things get magnified and grow.
This isn't to say we should ignore the flaws. We need to see them to improve or protect ourselves from potential danger. However, the focus needs to be balanced and tilted in the favor of the positive as much as possible.
You will be a better leader, employee or candidate for a job when your view of the world is framed from the positive.