I'm not entirely sure what you mean by "linking" the intro and conclusion of an essay. But, definitely don't feel that yo uneed to explicitly refer back to the opening idea in the last paragraph of your essay. This is especially true in very short essays, like what you will write for an HBS application. You do want the end of the essay to feel like it fits with the intro, but you don't need to explicitly link to the intro to make this happen!
If you'd like more help on this matter, I recommend our MBA Game Plan essay service.
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