which one did you have in mind?
HBS essays do not, in most cases, get you in. A bad essay — one that is annoying, mannered, odd, un_PC, or magnifies other boo boos in your app–can keep you out.
As to essays in this article that you may not think are super, the answer is that writer was otherwise qualified by dint of normal criteria–stats, work history, recs. etc. and high in his or her bucket [white male bankers, URM consultants etc] and the essay did no real harm and supported other things in the app.
That is also how Stanford works altho that essay is more easily mangled and does you harm, and of course, Stanford is REAL hard to get into in any case.