Why did the blue flower in Novalis’s Heinrich von Ofterdingen become a symbol of Romantic longing?

In the fragmentary novel Heinrich von Ofterdingen (1802) by Novalis, the blue flower (blaue Blume) first appears to the protagonist in a dream. The hero associates this mystical object with the woman he loves from afar, establishing it as a powerful symbol of longing.12

The blue flower became a widely recognized emblem among the Romantics because it perfectly encapsulated the movement's core interests. German Romanticism emphasized intuitive modes of thought—such as dreams and the unconscious—over pure rationalism. By representing an unattainable, idealized object of desire, the blue flower mirrored the characteristic Romantic motifs of inchoate longings, a melancholic sense of loss, and the pursuit of a higher, more complex understanding of reality.132