There's a belief that Dobby broke a promise when he saved Harry Potter's life at Malfoy Manor, but that wasn't necessarily the case. Here's why.
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Why did Dobby help Harry in Deathly Hallows when he was told not to by Harry? - Quora
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Plot Holes In The Harry Potter Series We Just Can't Ignore
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Why did Dobby help Harry in Deathly Hallows when he was told not to by Harry? - Quora
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Harry Potter and the Deathly Hallows: Part 1 (2010) - Plot - IMDb
In Harry Potter and the Chamber of Secrets, why did Dobby bother to warn Harry of the 'danger' at Hogwarts beforehand, even though Harry wasn't a muggle-born. Shouldn't he have warned Hermione