The story
Likely US origin, or possibly from Ivan Andreyevich Krylov's 1814 fable, The Inquisitive Man, which tells of a man going to a museum and noticing all sorts of things apart from an elephant.
Etymology from Wiktionary, CC BY-SA 4.0.
elephant in the room
Today it means: A problem or difficult issue that is very obvious, but is ignored for the convenience or comfort of those involved. Full definition →