To keep within Christian ideology: we are here in this world, with the "knowledge" of good and evil. You cannot have a concept of good without being able to identify it against the concept of evil. I often wonder that outside of this realm, the aspects of "good and evil" are not so important and ominous.
Here there is this duality, and we must "choose" a side it seems. As you indicate, every action - big AND small - is a choice to do "good" or "evil, and being a "good" or "evil" person is not as obvious as they make it seem in the movies.
One confusing part of the dichotomy is that nobody can be either good or evil... only actions can be judged. For example Hitler (the posterboy for evil) loved children and dogs... does that make him good or evil? Neither, only a flawed human being... much of what did politically was beneficial for Germany (but bad for the rest of Europe).