This brings to mind a realization I had a short while ago.
I was driving long distance for work and was on 2 lane divided highway. There was a flatbed truck ahead of me and I could see another flatbed truck ahead of it. They were going below the speed limit so after a bit of time losing patience I took the left lane to pass them. I started passing the closest truck and the thought struck me that this truck had been gaining on the truck ahead of it - perhaps it was the truck in front that was going slow and was holding up this truck, in which case this truck's driver might be preparing to pass the first. Thinking there was some chance the driver might not notice me alongside passing, I pushed down on the gas to pass that much quicker, to get within their field of vision from their side window and get beyond them as quickly as possible. When I pulled up beside this truck I found there was no truck ahead of it. Empty highway, and there was nowhere the first truck could have turned off. The foremost truck just disappeared.
When I told my wife this story when I later got home, she expressed concern about these sort of changes happening when I am driving (similar abrupt changes in traffic had happened before, and also when I was a pedestrian walking to work). It was then that I realized that these changes always seemed to occur in ways that decrease risk. They've never occured that there was suddenly a car closer than expected or appeared out of nowhere - it was always that cars were suddenly further away or disappeared.