[CKKim]

Indeed. Reading the Wikipedia entry on Cassagnes I wonder: 'idea' or 'discovery'?

"Cassagnes, an electrician at the Lincrusta Company, was performing a routine installation of a factory light switch plate wrapped in a translucent decal covering. During the installation, he removed the decal and wrote on it with a pencil, noticing that image transferred to the opposite face. Cassagnes tinkered with his discovery, which led to the world's first prototype of the Etch A Sketch."

I love these stories of something chanced upon by accident being turned into a product. It wouldn't surprise me if most successful ideas come about this way, rather than from a 'visionary' entrepreneur brainstorming the 'next big thing'.