Harry said in THE DEATHLY HALLOWS that the Patronus Charm was the only spell Hermione was bad at,despite her producing a fully-fledged Patronus in the DA. This may be because Hermione has a 'fear of failing' that isn't visible in Harry. It may be that a happy memory is not the only thing that is needed to produce a Patronus-confidence may also be handy.
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Interesting facts about Harry Potter that you didn't know(or maybe you did!'
Non-FictionHere you'll find a list of things that you probably didn't know. Disclaimer-I own nothing.