The fact that I am explicitly not giving you information gives you information.
In drafting a post, I wanted to avoid spoiling something, one of those cases when you want to recommend something without saying why so that someone can experience the rare joy of having all the surprises. “Just go watch/play/read it. It’s that good, and I don’t want to spoil anything for you.”
But now you know there is something to be spoiled. If it were a mystery, and I said I did not want to spoil the ending for you, that would not be new information; you expect there to be a big reveal at the end. If it is an action movie, and I tell you I want to avoid spoiling the ending, that immediately tells me the ending is not “the hero kills the bad guy, gets the girl, and saves his child.” If I tell you I cannot tell you anything about it at all, that tells you it will be a deconstruction, mind screw, or otherwise filled with twists and not what it seems. The content of the surprise can still be a surprise, but knowing that a surprise is coming makes it less surprising, and your suspicious mind starts looking for clues that might have passed you by if you were not primed to expect a twist.
At some point, it becomes fair game. If you do not know about Rosebud or Luke’s father, sorry, those are public information. By now, you know that Bioshock and Portal have big surprises at their midpoints, even if you do not know what those are (and you probably know).
But how do you protect the secret without revealing the fact of the secret, other than just lying about it?