The mind must be given relaxation- it will rise improved and sharper after a good break. Just as rich fields must not be forced- for they will quickly lose their fertility if never given a break- so constant work on the anvil will fracture the force of the mind. But it will regains its powers if it is set free and relaxed for a while. Constant work gives rise to a certain kind of dullness and feebleness in the rational soul.
— Seneca, On Tranquility of Mind 17.5 —