We begin teaching 'opposite' to students in kindergarten. It is not difficult. The students learn the concept quickly and enjoy the games we create using opposites. The skill is reviewed in first and second grade. By that time the students have a firm grasp on the concept and it's not necessary to revisit it in the classroom. Somehow adults don't seem to grasp the concept as easily.
It is physically impossible to go in two directions at one time. One cannot go east and west simultaneously.