Why are headlight beams more visible on foggy night than on clear night?

Light from your headlights goes out from the lamps with no material to hit until it reaches the ground or an object in front of you.

In foggy weather there are millions of tiny water droplets in the air. Some of these droplets reflect the headlight beams and shows us the overall path. This is what causes that overall path of your headlights showing up so well on a foggy evening.