Recognition is deceptive
Reading something we have previously read about feels like we encounter something we already know. This comfortable feeling deceives us. The test of knowledge isn't in the feeling of recognition. If we've never otherwise retrieved this thing from memory, we won't when it counts.
From Book: A Mind for Numbers:
We don’t engage in passive rereading because we are dumb or lazy. We do it because we fall prey to a cognitive illusion. When we read material over and over, the material becomes familiar and fluent, meaning it is easy for our minds to process. We then think that this easy processing is a sign that we have learned something well, even though we have not.
It gets worse the more often we're exposed to the same story, as we'll less and less feel the need to put in the effort and ask questions about it to commit it to memory for real.
Related: mere-exposure effect / Zeigarnik effect