Tom Waits quoted in The Word magazine.

“Some songs,” he has learned, “don’t want to be recorded.” Fortunately, he says, other songs come easy, like “digging potatoes out of the ground”. Others are sticky and weird, like “gum found under an old table”.
Clumsy and uncooperative songs may only be useful “to cut up as bait and use ’em to catch other songs”. Of course, the best songs of all are those that enter you “like dreams taken through a straw”. In those moments, all you can be, Waits says, is grateful.

From an original article by Elizabeth Gilbert in American GQ.
The whole GQ interview is here – I’m not linking to the GQ site because it’s shit, and apparently in german.