A "Hook" in my mind is also something that makes your candidate different. Sometimes it can be an adversity that was overcome. IE: one young man that we were helping was home schooled. One morning during his senior year his Mother dropped dead in front of him, with a heart attack. He went and got a Job and helped support his family while Dad was in a bad way. Later he got himself enrolled in a private school, having earned his own tuition and re-did Junior and Senior Year. . . . played Football etc... So a great story, that drew people in.
We live Rural, so a great lack of AP courses, limited clubs and activities, poor academics, etc...My Son wrote his essay about working Cattle and how staring down an angry Bull gave him courage to be a soldier, also how he felt like the "Service Academies" were for those other types of Kids, until he began his quest and realized that he could be that kind of leader that was needed. I believe that his quiet humility and dignity, together with Letters that stressed his compassion and caring for fellow students (He leads from the middle) caught their interest.
So a "Hook" while it may sound callous, is a marketing angle. What makes "YOU" Different, from all those others.
High grades and test scores are a big yawn to these folks, they see them all day long.
I want to believe that they are also looking for that Kid who slows down, paces, and encourages that lagging exhausted Plebe, VS that natural athlete who races ahead finishes first and then stands there looking smug while everyone else drags in. Probably just kidding myself there.