Dementia science has developed some remarkably sophisticated tools with the aims of understanding the course of the underlying neurodegeneration and opportunities to prevent it or slow it down.  Despite valiant efforts to portray the findings in the light of a, favoured, disease model, the factual results don’t fit in. Interventions that should have worked, don’t. Among the early promises was that negligent, and therefore preventable,  triggers of dementia would be identified. Traumatic brain injury and sports concussion were presumed to be among them. The purpose of this paper is to explain: the important factual results, what really does link brain trauma and dementia and why some people develop dementia while others do not. The explanations are obvious in retrospect and provide a strong narrative basis for expert testimony in dementia liability claims. At present, and increasingly clearly, the science indicates no causal link between either brain injury or concussion and s