I guess it depends on your scenario...
If you were personally in a position to change the outcome, then you can speak from that perspective and discuss how your actions, if different, could have had an effect.
If, on the other hand, you were following someone else's lead and didn't have the authority to really change how the group or team handled things, then the essay could be more diagnostic about what the team could have done differently, or you could discuss how you could have spoken up and offered a different course of action, regardless of whether it would have been followed.
My sense is that adcom doesn't always have a set answer they're expecting. If you tailor it to the specifics of your experience and get to the heart of what they're really after, which I assume is the ability to self-diagnose and learn from mistakes, you'll probably be alright.