Self-esteem coupled with a good bit of social anxiety.
Luckily this one is easy to fix. Next time you’re in public, try this. For like 2 minutes, force yourself to do this, hold your head up high, look people in the eye, and don’t look away when they meet your gaze. Instead smile. Maybe nod a little. Do this once a day until it stops being awkward. Then do it all the time.
I’m not gonna lie, it’s gonna suck at first. But there’s a trick to it. Don’t think in your head while you’re doing it. Focus on your actual body sensations. It tends to crowd out the negative anxious feedback loop if what you’re worried about is the mechanics of actually holding your head up high or the specific muscles you’re using to smile. And the people you’re smiling at won’t know the difference.
This little practice can change your life.