When visibility is poor, people have car accidents because they can't see what's ahead of them, right? Actually, the Mandelbaum Effect implies that sometimes people have accidents because they aren't even looking for what's ahead of them.
Most drivers have, at least once, experienced what it's like to drive in bad visibility. A violent rainstorm, a patch of fog, or all of the windows suddenly fogging up simultaneously. Pretty scary, right? When it's not safe to stop suddenly, we are forced to peer anxiously out into the blur, trying to pick out the road and the other cars until we can pull over.
Sometimes stopping isn't an option. That gets dangerous, and not just because we can't see what's on the road. When the world blurs up on us, unless we make a conscious effort to keep focusing far off into the distance, our eyes focus nearby. Generally, the distance we focus on is just under a meter away from us, and it doesn't matter if something's there to look at or not.
The phenomenon, discovered by J Mandelbaum in 1960 and called the Mandelbaum Effect, happens when we get hit with snow, rain, fog, or even when we get dirty windows. Anything that turns the landscape fuzzy can bring it on. It's not a conscious decision or carelessness. Nevertheless, it makes for accidents because the driver often isn't even aware that something's ahead of them until they're in an accident.
A scary prospect for drivers, it's even scarier for pilots, who deal with fog and clouds, and who don't have the option of pulling over. Some people have less of a propensity for the Mandelbaum Effect than others. Although it's possible to test for it, no one quite knows how to compensate for the effect yet.
[Source: The Mandelbaum Effect]