The word 'disillusionment' captures that moment when the shiny veneer wears off and reality hits hard. It's not just disappointment—it's the crumbling of deeply held beliefs or ideals. Like when a childhood hero turns out to be flawed, or a long-awaited sequel butchers everything you loved about the original.
English literature often portrays this through characters like Holden Caulfield in 'The Catcher in the Rye', where youthful idealism collides with adult hypocrisy. The term implies a permanent shift in perception, different from temporary letdowns. There's an almost grieving process for the truth you wish you hadn't discovered.