"The dog is running here and there."
Translation:Hunden løper hit og dit.
The way I get it, and it usually works out fine for me, is that it's all about the verb itself.. See, verbs like run or walk, or go, they imply motion themselves, hence the "directional hit and dit", while verbs like be (is) or lie (down) indicate static situation, and therefor the "static her and der" Hope that helps
Because the point of the phrase is to show that there's static adverbs (her, der = here, there) and motion adverbs (hit, dit = hither, thither) and they're different. Otherwise people will just ignore them altogether and say "her" and "der" to mean both (just like in English) and that would be wrong.