“For all we live to know is known.”

“And boyhood is a summer sun / Whose waning is the dreariest one-- / For all we live to know is known, / And all we seek to keep hath flown--”

“Since we cannot know all there is to be known about anything, we ought to know a little about everything.”

“Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns- the ones we don't know we don't know.”

“And for once, Donald Rumsfeld, in the news at the time over the Iraq war made sense to me: "As we know," he said, famously, "there are known knowns-things we know we know. We also know there are known unknowns-things we know we don't know. But there are also unknown unknowns- things we don't know we don't know.”

“There are some people that we know all our lives and yet never really feel we know them at all. But there are other people—” Unable to resist the temptation, he ran a feather-light caress down the curve of her cheek with one leather-sheathed knuckle. The cobalt depths of her eyes flickered with response, but she said nothing, heeding his every word. “—people we meet in a day, and instantly, it feels as though we’ve known them all our lives.”