figment of (one's)/the imagination

An experience that initially is thought to be real but is actually imagined. I thought I heard the sound of my front door opening last night but it turned out to be a figment of my imagination. I really thought Callie liked me, but I guess it was a figment of my imagination if she's asked John to the dance instead. A: "Where did that file go? I could have sworn I left it right here." B: "Guess that was a figment of the imagination."

figment of the imagination, a

An imaginary occurrence; a pipe dream. This expression is tautological, since figment means a product of fictitious invention. Nevertheless, it has been used since the mid-nineteenth century. It appeared in Charlotte Brontë’s Jane Eyre (1847): “The long dishevelled hair, the swelled black face, the exaggerated stature, were figments of imagination.”