Distance is a scalar quantity that tells you how far you ran around the house - that's your 400 meters. Since it's a scalar, the direction you ran is irrelevant. The only thing that matters is how far you traveled. But displacement is a vector quantity and measures the difference in your position from where you started to where you ended, and if you finish up in the same place you started, your displacement is zero. The direction or directions you ran does have an impact on your displacement because displacement is a vector. Vectors are represented diagrammatically with an arrow. A long arrow represents a big number, and a small arrow represents a small number.