The Chesterton version looks like it was designed to poke the older (and in my opinion better) advice from Lord Chesterfield:
Whatever is worth doing at all, is worth doing well.
Or, rephrased as Simon did:
Anything worth doing is worth doing well.
I strongly recommend his letters to his son. They contain quite a bit of great advice- as well as politics and health and so on. As it was private advice given to an heir, most of it is fully sound.
(In fact, it's been a while. I probably ought to find my copy and give it another read.)
Ah, I was gonna mention this. Didn't know it was from Chesterfield.
I think there'd be more musicians (a good thing IMO) if more people took Chesterton's advice.
Here's the new thread for posting quotes, with the usual rules: