My hypothesis regarding the placebo effect - Why optimistic people are happier and more successful

For those who don't know what a placebo is, check out my earlier post: http://thebeautyofmedicine.blogspot.com/2014/01/the-placebo-effect-and-its-possible.html

So after doing some thinking, I hypothesized that optimistic people are releasing dopamine at higher levels than pessimistic people. This then leads to my next part of my hypothesis, which is that people who are optimistic people have a higher chance at success than those who are pessimistic.

So how did I arrive to this? Well first, since dopamine is associated with happiness and pleasure, it causes people to be more optimistic. This is because optimistic people often perceive the glass as half-full and are thus always looking at the positives in life, thereby being happier and resulting in a higher release of dopamine at any given point in time. 

Before and as you are taking a test, when you constantly say that you are going to get and 'A,' your body gradually releases more and more dopamine during the test, which serves as a motivation to do better and closer to achieving your goal. Thus, statistically speaking, optimistic people would theoretically come closer to achieving their goals then pessimistic people. Of course, there is the possible case that an unrealistically optimistic person is completely let down by his/her unrealistic goals (such as test results), and this backfires in that there is a dopmaine decrease since the person does not get the award he/she expected. I noticed the possibility of this 'backfiring' after reading this abstract: http://www.ncbi.nlm.nih.gov/pubmed/22795698

I wish I had the resources to conduct such experiments to test these kinds of hypotheses... I guess I have to be patient and wait for the time to do so :/