The Way You See Yourself
Most people are wired to see imperfections in themselves. Your confidence can fall so low that you only see beauty in others and never in yourself. Your observations become so acute that you spot every tiny imperfection: how you look, which part of your body is oddly shaped, how you speak, where you falter, and how embarrassing you think you are in front of others.
When someone points out that you are focusing too much on your imperfections, you cannot process it because, to you, it's true. You aren't lying. And that is true, but you are ignoring a simple fact: what you are noticing doesn't matter. Everybody's body is oddly shaped in one way or another, aside from obvious physical defects. The only thing that truly matters is what you choose to see in the mirror.
What you feel also determines what you see in the mirror. When you look at yourself, do you see a handsome man, or do you see someone who is pathetically ugly? Do you consider yourself stupid or a genius? The problem lies at both extremes. Excessive self-aggrandizement is just as inaccurate as relentless fault-finding. If you are hell-bent on finding flaws within yourself, you will eventually find them because the human mind is wired to serve your expectations.
You cannot change your genetics, but everything else is up for grabs. You can improve your grooming. Reinvent yourself by working on your hairstyle, your beard if you are into that, and, most importantly, refreshing your wardrobe. Wear clothes that suit your body. This matters because it shapes people's perception of you. Be polite and courteous. Always greet people with a smile.
This sounds clichéd, and to some extent it is. But think about why these ideas have become clichés. It is because they have been producing results ever since people discovered that Dale Carnegie was right when he wrote How to Win Friends and Influence People. Develop a personality worth talking to. Whether you are short on looks or not, you need a personality because looks may earn you momentary attention, but anything beyond that requires character, manners, and substance.
Your opinion of yourself comes from the gap between your potential and your reality. Shorten that gap as much as possible. Take yourself seriously. Keep developing new skills that enrich your personality and expand your capabilities. You naturally feel better about yourself when you become better in reality. Positive feedback from others simply becomes the icing on the cake.
This creates a virtuous cycle: you work on yourself, you develop a healthier self-image, people respond to you more positively, and that encourages you to keep improving. Over time, confidence stops being something you pretend to have. It becomes a natural consequence of becoming the person you know you are capable of being.