The real reason is that the everyday world is isolated from the quantum world. An apple falling from a tree gives the non-scientist a handle for understanding gravity’s universal action. No such clear image comes to mind when we think of quantum processes. The strange behavior of subatomic particles doesn’t translate into how objects behave all around us. For decades quantum theory has tried to build a bridge between daily existence (described by classical physics) and the shadowy, seemingly alien world that nevertheless gives rise to everything in existence (described by quantum physics).
It’s no easy task, and even physicists who realize that all matter boils down to invisible clouds of probability still go to work driving a car, which behaves like a normal tangible object, not a cloud. How are we to understand quantum reality as our reality, too? A single word may hold the key: interaction. In the classical world (i.e., everyday reality) everything is built from small units interacting to form something larger. Society is built from the interactions of individuals; thoughts are built from the interaction of neurons in the brain; even a sand dune cannot form unless grains of sand interact with each other. As a fact of Nature, nothing is more obvious. The Mona Lisa is a work of genius, but it wouldn’t exist if molecules of paint didn’t interact with the canvas, causing the two to adhere. When Da Vinci tinkered with this process, his masterwork, The Last Supper, started to flake and crumble only a few years after its completion.