Fog shrinks the world to a circle about fifty metres wide. Beyond that, the road simply stops, and every tree and bend arrives out of nowhere.
It sounds unsettling, and on a busy road it would be. On an empty forest road it is the most peaceful riding I know: no views to chase, no summit to reach, just the next fifty metres.
You cannot rush a ride you cannot see the end of.
Bright lights front and back, even in daylight, and a slower pace on the descents. That is all it takes.