What you are saying is that a certain personality under a certain set of circumstances will perform a certain action. However, no two of us will ever have the same brain chemistry, DNA and circumstances as any of our counterparts. We define, therefore, what we will do in certain situations--no one else sets a precedence for our own actions. We are also highly inconsistent in our choices. How many times have you eaten different things under the same circumstances? We are guided by our environment and heredity, but we ultimately have the choice of what we are and what we will do. I believe we can actually change our brain chemistry by what we choose to focus on--we're not merely mechanical products of our surroundings.