Another way to look at questions like this is that you can expect failure and disappointment at some point in med school (not necessarily failing an exam but failing to get a High Pass in a rotation that you felt you did well in, or not being selected for a specific training program) and what the adcom would like to know is how you have dealt with such disappointments and failures in the past. How do you change the things you can, accept the situations you can't change, and how do you tell one from the other?
In other words, the adcom may be less interested in what the failure WAS and more interested in what you did about it.