The Power of Fish
This is possibly the single most profound passage in Thinking, Fast and Slow, Daniel Kahneman's memoir cum valedictory survey of cognitive biases. He's recounting a year that he spent working in Vancouver:
The Canadian government's Department of Fisheries and Oceans had a program for unemployed professionals in Toronto, who were paid to administer telephone surveys. The large team of interviewers worked every night and new questions were constantly needed to keep the operation going. Through Jack Knetsch, we agreed to generate a questionnaire every week, in four color-labeled versions. We could ask about anything; the only constraint was that the questionnaire should include at least one mention of fish, to make it pertinent to the mission of the department.
"Always make sure there's at least one mention of fish." This is, somehow, a metaphor for the entire human condition. Explaining this is left as an exercise for the reader.