I suppose it depends on how one feels about the relationship themself. There could be a sense of relief if they were thinking along the same lines but did not know how to go about approaching the subject.
More often than not most relationships that end have some (clues or warning signs) that all was not right in paradise. People just tend to ignore issues or adopt a "go along to get along" strategy until they either can't take it anymore or someone else comes along. My point is most of the time a break up is not a "complete shock".
When someone is caught off guard or they thought everything was perfect odds are they will ask "why?" and then offer to "change" in order to keep the person they love in their life.
Honestly though we're all looking for someone who loves and appreciates us for who we are.
The only logical thing to do is accept it's over and move on.
It may hurt in the short run but an ex is usually an ex for a good reason.