What did Koriat & Bjork (2005) show with "foresight bias"?

Studying with the answer visible makes you overrate how well you'll recall it later, when the answer will be absent.

Koriat & Bjork (2005) had people study cue–target pairs (e.g. a word and its associate) with the target sitting right there, then predict their own future recall. Because the answer was present, it felt obvious and reachable, so predictions ran high — but at test the answer was gone, and recall fell well short of those predictions.

They called it "foresight bias": at study time you can't un-see the answer, so you can't imagine the difficulty of retrieving it without it. This is a core reason re-reading feels like enough. The material is in front of you the whole time, so nothing ever feels hard.