I have two people. Fred knows something about X. Jim is curious how much Fred knows. Fred has also made some wrong assumptions about X.
In describing the scene, I wrote this:
Perhaps Fred didn't know as much as Jim hoped he knew, and had made some wrong assumptions.
Then I thought about whether the pronouns and ordering had made it ambiguous. In the sentence, is it clear that hopes are Jim's, but they are hopes about Fred's knowledge; and is it clear that the wrong assumptions are (a) part of the "perhaps", and (b) belong to Fred?
In trying to re-write it to make it less ambiguous, I lose some of the flow.