T.S. Eliot has perhaps the best explanation of that phenomenon:
Schrodinger's cat's a mystery cat, he illustrates the laws;
The complicated things he does have no apparent cause;
He baffles the determinist, and drives him to despair
For when they try to pin him down—the quantum cat's not there!
Schrodinger's cat's a mystery cat, he's given to random decisions;
His mass is slightly altered by a cloud of virtual kittens;
The vacuum fluctuations print his traces in the air
But if you try to find him, the quantum cat's not there!
Schrodinger's cat's a mystery cat, he's very small and light,
And if you try to pen him in, he tunnels out of sight;
So when the cruel scientist confined him in a box
With poison-capsules, triggered by bizarre atomic clocks,
He wasn't alive, he wasn't dead, or half of each: I swear
That when they fixed his eigenstate—he simply wasn't there!
—from Old Possum's Book of Quantum Vivisection