"Thou shalt not overspend" is rapidly becoming a tenet of the evangelical belief system, rivaling social issues like gay marriage.
Or it might make you overspend on cars and helicopters and lead you to early, penniless death.
1610s, "to wear out," from over- + spend. Meaning "to spend more than is necessary" is attested from 1857. Related: Overspent; overspending.