The Imagination merely enables us to wander into the darkness of the unknown where, by the dim light of the knowledge we carry, we may glimpse something that seems of interest. But when we bring it out and examine it more closely it usually proves to be only trash whose glitter had caught our attention. Imagination is at once the source of all hope and inspiration but also of frustration. To forget this is to court despair.

The Art of Scientific Investigation (ed. 1950)