Rhythm of War (The Stormlight Archive, #4)

by Brandon Sanderson

Imagine you had two pieces of cloth, one red, one yellow. Before you and your brother parted, you each reached into a bag and selected one—but kept it hidden, putting it away in a box, unseen. You parted, traveling to distant quarters of the land. Then, by agreement, let us say that on the same day at the same time you each opened your box and took out your cloth. Upon finding the red one, you’d instantly know your brother had found the yellow one. You shared something, that bond of knowledge—the Connection exists, but isn’t something that can necessarily be exploited.

Hmm, I guess we're learning about quantum entanglement today.