Friend or foe.
Fish or fowl.
Person or thing.
These pervasive conundrums all seemingly suggest that we at times are faced with a dichotomous situation and need to choose one facet or the other. Life might force us to contend with circumstances that consist of two mutually exclusive options. In more flavorful language, you could suggest that an exclusionary binary equation requires us to starkly go marching down one distinct path rather than another.