Source: The Chronicles of Prydain (1964–1968), Book IV: Taran Wanderer (1967), Chapter 19 (Annlaw)
Quotes from book
Taran Wanderer

Taran Wanderer is a high fantasy novel by American writer Lloyd Alexander, the fourth of five volumes in The Chronicles of Prydain. The series follows Taran, the Assistant Pig-Keeper, as he nears manhood while helping to resist the forces of Arawn Death-Lord.
“If I fret over tomorrow, I'll have little joy today.”
Source: The Chronicles of Prydain (1964–1968), Book IV: Taran Wanderer (1967), Chapter 17 (Llonio)