“We will never recognize the true value of our own lives until we affirm the value in the life of others.”

Source: The Tao of Pooh

Remarks by President Obama at the 70th Anniversary of D-Day at Normandy American Cemetery and Memorial, Omaha Beach, Normandy, France at June 6, 2014 http://www.whitehouse.gov/the-press-office/2014/06/06/remarks-president-obama-70th-anniversary-d-day-omaha-beach-normandy
2014

Psychomagic: The Transformative Power of Shamanic Psychotherapy (2010)

Le Commerce et le Gouvernement (1776), as quoted in Marx's Capital, Vol. I, Ch. 5.

Variant: We do not place especial value on the possession of a virtue until we notice its total absence in our opponent.
Source: Human, All Too Human

Nobel lecture (1970)
Context: The divergent scales of values scream in discordance, they dazzle and daze us, and in order that it might not be painful we steer clear of all other values, as though from insanity, as though from illusion, and we confidently judge the whole world according to our own home values. Which is why we take for the greater, more painful and less bearable disaster not that which is in fact greater, more painful and less bearable, but that which lies closest to us. Everything which is further away, which does not threaten this very day to invade our threshold — with all its groans, its stifled cries, its destroyed lives, even if it involves millions of victims — this we consider on the whole to be perfectly bearable and of tolerable proportions.

Source: Robinson Crusoe (1719), Ch. 10, Tames Goats.

Source: Mastery