Grief and disappointment give rise to anger, anger to envy, envy to malice, and malice to grief again, till the whole circle be completed. - David Hume

And why should man, added he, pretend to an exemption from the lot of all other animals? The whole earth, believe me, PHILO, is cursed and polluted. A perpetual war is kindled amongst all living creatures. Necessity, hunger, want, stimulate the strong and courageous: Fear, anxiety, terror, agitate the weak and infirm. The first entrance into life gives anguish to the new-born infant and to its wretched parent: Weakness, impotence, distress, attend each stage of that life: and it is at last finished in agony and horror.

How little is requisite to supply the necessities of nature? And in a view to pleasure, what comparison between the unbought satisfaction of conversation, society, study, even health and the common beauties of nature, but above all the peaceful reflection on one's own conduct: What comparison, I say, between these, and the feverish, empty amusements of luxury and expense? These natural pleasures, indeed, are really without price; both because they are below all price in their attainment, an above it in their enjoyment.

starting with Martin Luther’s rebellion against the Church of Rome in 1517, led to widespread religious wars founded on philosophical differences: one side took Church authority and tradition as the criterion of truth, the other appealed instead to the Spirit of God acting within the individual believer.