I always think this quote has explained a related topic the most concisely: "It is difficult to get a man to understand something, when his salary depends upon

I always think this quote has explained a related topic the most concisely: "It is difficult to get a man to understand something, when his salary depends upon his not understanding it!" - Upton Sinclair, "I, Candidate for Governor: And How I Got Licked" (1935)