Do you have any idea how difficult it is to forget the interpretation of a parable that you've been taught? It's ingrained in the mind. It becomes part of the vocabulary of belief, and in turn it becomes belief itself.
I'm working through parables at the moment, attempting to read with fresh eyes. It's all too easy to keep reading them as they were explained to me years ago.
Whenever I see them in a new light, it's often because I've learned something about the culture of the time, something relevant to the parable. Historical criticism to the rescue! Without that background, the parable is a translation of an alien idea from an alien time in an alien place. It's a mystery waiting for an explanation.