“The uttered part of a man's life, let us always repeat, bears to the unuttered, unconscious part a small unknown proportion. He himself never knows it, much less do others.”

Lovelock (1994)

trans. Jasper Hopkins (Minneapolis: Arthur J Banning Press, 1990), 119 – 20.
De Docta Ignorantia (On Learned Ignorance) (1440)

Source: Never Let Me Go

Rawstory.com Interview (9 September 2005) http://rawstory.com/news/2005/Zinn_interview_part_two_Same_arguments_made_in_Vietnam_made_0909.html, which compares U.S. wars in Iraq and Vietnam
Context: I would encourage people to look around them in their community and find an organization that is doing something that they believe in, even if that organization has only five people, or ten people, or twenty people, or a hundred people. And to look at history and understand that when change takes place it takes place as a result of large, large numbers of people doing little things unbeknownst to one another. And that history is very important for people to not get discouraged. Because if you look at history you see the way the labor movement was able to achieve things when it stuck to its guns, when it organized, when it resisted. Black people were able to change their condition when they fought back and when they organized. Same thing with the movement against the war in Vietnam, and the women's movement. History is instructive. And what it suggests to people is that even if they do little things, if they walk on the picket line, if they join a vigil, if they write a letter to their local newspaper. Anything they do, however small, becomes part of a much, much larger sort of flow of energy. And when enough people do enough things, however small they are, then change takes place.

Source: The Devil's Arithmetic (1988), p. 143

The Fifteenth Revelation, Chapter 65

Sam Harris, "Death and the Present Moment", speech at the Global Atheist Convention (April 2012) http://www.youtube.com/watch?v=ITTxTCz4Ums&t=17m52s
2010s
Context: Most of us do our best not to think about death. But there’s always part of our minds that knows this can’t go on forever. Part of us always knows that we’re just a doctor’s visit away, or a phone call away, from being starkly reminded with the fact of our own mortality, or of those closest to us. Now, I’m sure many of you in this room have experienced this in some form; you must know how uncanny it is to suddenly be thrown out of the normal course of your life and just be given the full time job of not dying, or of caring for someone who is... But the one thing people tend to realize at moments like this is that they wasted a lot of time, when life was normal. And it’s not just what they did with their time – it’s not just that they spent too much time working or compulsively checking email. It’s that they cared about the wrong things. They regret what they cared about. Their attention was bound up in petty concerns, year after year, when life was normal. This is a paradox of course, because we all know this epiphany is coming. Don’t you know this is coming? Don’t you know that there’s going to come a day when you’ll be sick, or someone close to you will die, and you will look back on the kinds of things that captured your attention, and you’ll think ‘What was I doing?’. You know this, and yet if you’re like most people, you’ll spend most of your time in life tacitly presuming you’ll live forever. Like, watching a bad movie for the fourth time, or bickering with your spouse. These things only make sense in light of eternity. There better be a heaven if we’re going to waste our time like this.

Credo (1965)