Aurea mediocritas

The golden mean in Latin is aurea mediocritas from Horace Odes 2. 10. 5.

Odes, Book II, X. Rectius Vives
Horace

Licinius, trust a seaman's lore:
Steer not too boldly to the deep,
Nor, fearing storms, by treacherous shore
Too closely creep.
Who makes the golden mean his guide,
Shuns miser's cabin, foul and dark,
Shuns gilded roofs, where pomp and pride
Are envy's mark.
With fiercer blasts the pine's dim height
Is rock'd; proud towers with heavier fall
Crash to the ground; and thunders smite
The mountains tall.
In sadness hope, in gladness fear
'Gainst coming change will fortify
Your breast. The storms that Jupiter
Sweeps o'er the sky
He chases. Why should rain to-day
Bring rain to-morrow? Python's foe
Is pleased sometimes his lyre to play,
Nor bends his bow.
Be brave in trouble; meet distress
With dauntless front; but when the gale
Too prosperous blows, be wise no less,
And shorten sail.