“…it is not necessary to accept everything as true, one must only accept it as necessary.”

As quoted in Margaret Mead : Some Personal Views (1979) edited by Rhoda Métraux
As quoted in American Quotations (1992) by Gorton Carruth and Eugene H. Ehrlich
1970s
Variant: At times it may be necessary temporarily to accept a lesser evil, but one must never label a necessary evil as good.

"Three Interviews" in Lyrical and Critical Essays (1970)

Source: Success! (1977), p. 284; a portion of this — "In order to succeed we must first believe that we can" — has become widely attributed to Nikos Kazantzakis on the internet, but without citation of any sources.
Context: The American system demands success, and in order to succeed we must first believe that we can. Yet our society, with its intolerance of failure and poverty, traps millions of people in positions where any kind of success seems impossible to contemplate, and in which failure itself is a kind of passive rebellion against their own misery and the social system which created it in the first place.
To succeed it is necessary to accept the world as it is and rise above it.

As quoted in "Some Szilardisms on War, Fame, Peace", LIFE‎ magazine, Vol. 51, no. 9 (1 September 1961), p. 79
The Voice of the Dolphins : And Other Stories (1961)
Variant: I'm all in favor of the democratic principle that one idiot is as good as one genius, but I draw the line when someone takes the next step and concludes that two idiots are better than one genius.

Pearls of Wisdom

Norway attack suspect had anti-Muslim, pro-Israel views http://www.jpost.com/International/Article.aspx?id=230762/ Jerusalem Post (24 July 2011)
Other

Silence Speaks, from the chalkboard of Baba Hari Dass, 1977
Context: Q: What can I do to overcome my fear of death? A: Attachment to the body causes fear of death. It is the strongest attachment. Even a newborn infant has this attachment. To overcome the fear of death it is necessary to accept that we all have to die. (p.39)