Idleness is the root of all evil.

Meaning: Lack of productive activity breeds vice, as unoccupied minds and hands naturally drift toward harmful behavior.

Origin: The saying dates from the early 15th century, and the idea is often credited to Saint Bernard of Clairvaux. An early 14th-century French saying held that idleness attracts vices, and Chaucer warns against idleness in The Second Nun's Prologue.