Turning and turning in the widening gyre
The falcon cannot hear the falconer;
Things fall apart; the centre cannot hold;
Mere anarchy is loosed upon the world,
The blood-dimmed tide is loosed, and everywhere
The ceremony of innocence is drowned;
The best lack all conviction, while the worst
Are full of passionate intensity.

William Butler Yeats (1865-1939) Irish poet and dramatist

“The Second Coming,” ll.1-8 (1920)
    (Source)

More examination of this quotation: The Best Lack All Conviction While the Worst Are Full of Passionate Intensity – Quote Investigator. See also Russell and Bukowski.