I feel a little bit different, from my understanding , the reason why you did not fully demostrated you potential was because of other people, or "outside" factors. Try to avoid blaming...My view is this is an essay to describe a case you made a mistake yourself or something like that. What they want to see is your cabability to know the weakness of yourself and how to learn from inperfection or failure.
The admin don't have an interest on something that you don't have the power to influence, what they are interested in is how you are going to improve YOURSELF from good to great :-) hope will be helpful