LotR -- Book 5 - Chapter 07 - The Pyre of Denethor

[Galadriel55]

Does it not bother anyone else that every time there is some surprise revelation Gandalf goes "Oh yeah, I knew that for a long time!". I think the only one he admitted to not knowing or suspecting was the Balrog. It bothers me, like he has to show that he knows best even though he didn't do anything about it when there was still a chance to prevent something. Denethor's palantir gazing was a topic of rumour as far as Rohan, though no one actually suspected a palantir (except know-it-all Gandalf of course). So if Gandalf thought this was the source of Denethor's knowledge and also his madness, could he have not used his suspicion to convince Denethor he is not all-knowing and all-powerful? Convince him that Gandalf can know something too, and through his own cleverness rather than a magic item? It's debatable if Denethor could have been scared or humbled into sanity or at least submission, but could Gandalf have at least tried? I'm not making a case against Gandalf here, but it just bugs me that - once again - he claims he suspected the thing after it happens.