I think Rumple’s style of learning was likely just to discover information and steal powers on his own, rather than having someone teach him. If you ask to be taught, it means you’re admitting you can’t figure something out yourself, and Rumple is loathe to admit that. Especially in FTL, he had a rep to build and uphold as an all powerful being to be feared. Sort of puts a dent in that if you then go around asking others to teach you things. It would mean exposing himself as having a weakness.
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