External resistance refers to the forces outside of you that create challenges to your quest for your best health. External resistance can arise from your environment, your social and family support structures, as well as the modern marketplace of goods and services that attempts to sell you products that can keep you trapped in poor health.
So many of the books written about health, nutrition, and weight loss are written as though the audience is professionals on these topics. Professionals like to write books to each other. We create our theories based on data, consensus, and professional interpretations. This is important work. And these books are very helpful.