It happened to me when I was reading a new edition of ”The Spoils of Poynton” by Henry James.

There was an essay in the beginning of the book that I started reading on inertia alone (yes, I know, I should have known better). In the first paragraph (maybe first sentence), it spoiled the dramatic ending.

Not only that, in the second paragraph it would give an interpretation of what that means. So I was robbed not only of the plot, but also of a interpretation of my own before reading it. I quit the book after those two paragraphs and never read it.