I don't know many people who are completely happy with themselves, do you?
Everyone I know has had times when they were down on themselves.
"I hate the way I look."
"Why do I always say such stupid things?"
"I just don't measure up."
We hit those troughs of low self-esteem when we just want to jump out of our own bodies and go inhabit some other more attractive, intelligent, successful person. Ironically, other people can view you as attractive and competent, but your view of yourself is entirely different.
For most people, the days when our self-image takes a nose dive are infrequent. We get back to the business of life and recognize we're not all that bad. In spite of our flaws and mishaps, we feel relatively confident in ourselves and what we can achieve.
But sometimes you can get stuck for months or even years in a deep hole of self-loathing and low confidence. You feel so bad about yourself that you stay contained in a tiny box of insecurity and fear.
The longer you stay in this box, the more you mentally reinforce your poor self-image. You feel so bad about yourself, you can't take action on anything. You're plagued with uncertainty, and you fear everyone is judging you and seeing you for the loser you think you are.
Eventually the whole mess becomes a self-fulfilling prophecy. People do start to view you differently because you think so little of yourself. This is a rugged hole to dig yourself out of. It's hard to take action and improve yourself when you feel like a speck of dirt.
But it is possible to dig yourself out of that hole and rebuild your self-esteem and confidence. It doesn't happen overnight, but if you're tired of feeling this way, and you're willing to take small but consistent actions, you can change.