“The essence of wisdom is to know when to be doing, and when it's useless even to try”
Source: The Last Enchantment
The Last Enchantment is a 1979 fantasy novel by Mary Stewart. It is the third in a quintet of novels covering the Arthurian legend, preceded by The Hollow Hills and succeeded by The Wicked Day.
“The essence of wisdom is to know when to be doing, and when it's useless even to try”
Source: The Last Enchantment