"Shame" is being filed under the Emotions section here because that's how it's typically thought of, but I don't think of it as an emotion. I think shame is a view of yourself as bad or simply unworthy. Emotions happen with it, of course--typically sadness and anxiety. When we say "I felt ashamed," that's often shorthand for "I saw myself as bad, and I felt (sad/anxious/etc.)."
Shame is very common. I think it's even somewhat encouraged in American culture. Yes, we also have the opposite emphasis ("I'm amazing!"), but we have plenty of shame. It's often labeled as "guilt," whether it's Catholic guilt, Jewish guilt, Protestant work-ethic guilt, secular guilt, generic guilt.... I think of guilt as a combination of feelings about a specific thing you've done, whereas shame is more a general sense about yourself.
Where Shame Comes From
I seriously doubt we're born viewing ourselves as bad or shameful. I think we tend to learn it from parents and others, usually while we're quite young. Some people aren't loaded up with much shame by their families, and they've got a shot at enjoying lots of healthy self-acceptance. Others were taught to be ashamed of themselves either all the time (ouch) or in some conditions... for example, if you aren't the smartest-prettiest-best / if you make any mistake / if you don't always take care of everyone / and so on. We learn shame when we're taught--directly or indirectly--that we're not worth much or that our worth hangs precariously from our latest accomplishments.
How To Reduce Shame
* First, commit to fighting the shame. Since it's actually seen by some people as virtuous to be down on yourself, you've got to decide to let yourself see yourself as good, or at least okay.
* Quit trying to earn self-acceptance. Try to view yourself as okay across the board. Yes, it still makes a difference what you do, but you love the person while still sometimes criticizing the specific behavior--just like you would (I hope) with your children. Try to be as kind and accepting toward yourself as you would be toward the person you love the most in the world.
* Sure, improve your behavior; just don't make your worth dependent on it (quitting smoking, getting a promotion, etc.).
* Read the article here on self-acceptance.
Licensed psychologist, Austin