"A well-fed man keeps and calmly gives forth his infinitesimal portion of eternity. It sounds big in the summer night. And it is, as it always was down the ages, when there was a man with something to tell, and ones, quiet and wise, to listen." - Ray Bradbury
To the extent that we can give a brief answer to the question of where novel ideas come from, it's curiosity. That's what people are usually feeling before having them.