Ok, well... my understanding of it is that nature is made up by random events. If those events were all there were, you'd get white noise. A perfectly even randomness. However, nature also has laws. With regard to sand, there's gravity, and slope, friction, etc... and that means these randomly falling grains of sand, on the macro scale, end up forming patterns. These patterns end up being very complex but predictable with statistics. Understanding a dune from the point of view of a grain of sand is nearly impossible. You just need to know the rules the system is following and then you can make accurate macro-scale predictions without having to compute every grain of sand in the dune.
The arguments made its way into nearly every branch of science now. Our attempts at brute forcing nature, and trying to connect the sub-atomic scale with the macro scale have mostly failed. But it now seems that maybe nature doesn't work that way. Nature seems more to work based on sets of probabilities, and particles seem to work more like "attributes" than matter. So perhaps the brain works like this to. It's a collection of chaos, bound by rules. Those rules cause the microscopic chaos to form patterns on the macro scale.