It is from this video. It is at 28 second.
Fiction often treats good and evil as uncrossing opposites.
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Sometimes it is not possible to say if two opposites are totally distinct or not. For example, black and white can be considered opposites, but they "overlap" in an infinite shades of gray.
Also, it is sometimes difficult to say if something is good or bad. Or if something is better to worse than something else.
In your sentence, there is a reference to a view where "good" and "evil" are totally unambiguous. Referencing geometry, there is no intersection (crossing) between the area of "good" and the are of "evil".