As a novice System Dynamicist one learns all the textbook rules and advice of system dynamics modeling. As a practicing System Dynamicist one learns the many shades of rules and advice. The latter ones are only occasionally spoken about and seldom written down. The experience gained from applying formal modeling technique to a diffuse ambiguous reality, often exist as vague mental models of the various roles a formal simulation model and a policy analyst can play in the public policy formation process.