I'll disagree.
Rule #1 in writing: Write about something you know ALOT about. There is NOTHING in the world a 17 knows more about than self. You are THE EXPERT. The great challenge is having the maturity and courage to write honestly, truth in lieu of fiction. USNA hates fiction (and ghost writers) and can spot both in the first 20 words.
And fortunately, that is precisely what USNA wants you to write about. You. No research notes. No footnotes. Gotta expose what YOU'VE discovered.
THE issue in this is "perspective." How and what one communicates about the one subject you are expert about @ age 17 or 18. What this means is determining not merely the "what" or even the "how", although those merit consideration. It is your POV, where are you going to "stand" to look at yourself and the scenario you choose as subject. What will you "see" and thus describe? What insight do you have about all of this. Don't get so caught up in the literal view.
Perhaps practice by having someone(s) who know you, posing real-life scenarios and asking you to "tell them a story" about that scenario lending some real "color" and insight to the story and particularly your role in that event.
Most candidates won't have spectacular, tragic, incredible moments ... and besides, that's not necessarily what plays in Peoria or in USNA admissions. It's the "how" you communicate as much or more of the "what". Too many get hung up on thinking they have to describe the moment they got to the top of Mt. Everest ... or was attacked by an elephant ... or won their first olympic medal at age 9 ... or ... you get the point. Sometimes the most mundane offers the best opportunity.
Curious: Can anyone provide the specific wording used in this year's questions?