This is a standard requirement of US commencement speeches, the deployment of didactic little parable-ish stories. The story thing turns out to be one of the better, less bullshitty conventions of the genre, but if you’re worried that I plan to present myself here as the wise, older fish explaining what water is to you younger fish, please don’t be. I am not the wise old fish. The point of the fish story is merely that the most obvious, important realities are often the ones that are hardest to see and talk about.
The author acknowledges the widespread use of didactic stories in commencement addresses in the United States, drawing attention to the instructive and parable-like aspects of these stories. This recognition gives the impression that the author is aware of the established rules in speeches of this kind and provides a clue that a deviation or unique perspective is on the horizon, so creating anticipation for what is to come. Consequently, it establishes the stage for an unorthodox investigation of the genre of commencement speeches.