I recently had the opportunity to view a marvelous motivational video -
What's right with the world
One of the main premises of the video is that what we believe affects our perceptions which become our reality.
I believe that we are in control of our own happiness (or lack thereof). That doesn't mean that other influences don't cause us pain or that we don't have problems which may seem insurmountable, it simply means we control how we react to them and we choose how to view them, as well as ourselves. I think we have 'internal tapes' that we play which affect our self-esteem, our ego, our confidence and our outlook on life. These tapes are a result of our life experiences and teachings.
Internal scripts that follow the lines of...I'm miserable, my life sucks, my husband/wife is the pits, I'm fat/ugly/short/weird/stupid and nobody likes me generally become self-fulfilling. Every time we tell ourselves that (or believe it when someone else says it), it is closer to becoming our reality.
I'm NOT a doctor, but from I've studied, I've come to think that in some cases, there IS a chemical imbalance which can be helped through medication(s). My understanding is that this type of chemical imbalance has physical effects such as lethargia, listlessness, lack of enthusiasm, sleep issues and a disruption of cognitive reasoning. But this does not change the fact that we are all responsible for ourselves and our belief patterns/perceptions.
I wrote an essay 20 years ago in which I described each person's life as a ship. We, as the captain, steer our ship with our choices. Just as a captain can't control the tides, the waves, winds or ice floes, we don't have control over the outside influences which affect our lives, such as illness, job loss, abuse, or traffic jams on the way home. We DO however, have control over how we choose to react to them. We can make a concious choice to have a positive outlook and to find the best in our world (instead of focusing on what's wrong).
As Rkzenrage says, it doesn't happen overnight. It took 20, 30, 40 years to learn those negative scripts and it will take a lot of effort and time to rewrite them. The habits of a lifetime are hard to break, but it can be done. Everytime I find myself blaming someone/something else for my own unhappiness, I shut off the tape and revise my response. I believe that with all problems that come my way, I can choose to accept the situation, change the situation or change my perception of the situation. This then, becomes my reality.
So, I think I'm thin. I'm really, really slender. That roll of fat around my waist? Is. not. there.

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Stormie