Published in 1855, H.G. Bohn's "Hand-Book of Proverbs" includes the one-liner,
An idle mind [brain] is the devil's workshop.
Variations on the theme include, "Idle hands are the devil's playground" etc.
It seems to me that an idle mind is never a problem.
It's a narrow mind that kindles the fires of hell.
And which of us does not have that problem?