If we could read the secret history of our enemies, we should find in each man’s life sorrow and suffering enough to disarm all hostility.
Henry Wadsworth Longfellow (1807–1882) American poet
“Table Talk,” Drift-Wood (1857)
(Source)
More discussion of this quotation here: If We Could Read the Secret History of Our Enemies, We Should Find in Each Man’s Life Sorrow and Suffering Enough To Disarm All Hostility – Quote Investigator.

