Polishing a turd
I try to stay away from idioms and other bits of faux-wisdom but one that actually stuck with me from recording/songwriting circles is â€œyou can't polish a turdâ€.
Which I always took to mean â€œif your song isn't any good, no amount of production or recording wizardy will make it goodâ€.
So episode 19 of season 6 of the Mythbusters is awesome: they polished some animal shit. Which may forever alter my songwriting process. Kudos.