Full Idea
Metrodorus says that all the wonderful, ingenious and brilliant inventions of the mind have been contrived for the sake of pleasure of the flesh or for the sake of looking forward to it, and any accomplishment not leading to this end is worthless.
Gist of Idea
All inventions of the mind aim at pleasure, and those that don't are worthless
Source
report of Metrodorus (Lamp) (fragments/reports [c.291 BCE], Fr 6) by Plutarch - 74: Reply to Colotes §1125
Book Reference
Plutarch: 'Moralia - vol 14', ed/tr. Einarson,B. /De Lacy P.H. [Harvard Loeb 1967], p.299
A Reaction
It is very hard to think of counterexamples! Would anyone bother to work out the theorems of number theory if they didn't enjoy doing it? Would any sensible person make great sacrifices if they didn't think that increased happiness would result?