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The Gen 1 Pokédex type distribution really affected my idea of some type matchups
>Thought Rock was inmune to Electric because so many Rock Pokémon in Gen 1 were also Ground
>Thought Plant resisted Fighting because most Plant Pokémon were also part Poison
>Thought Bug was weak to Ice because so many Bug Pokémon were part Grass or Flying
Also more generally, I used to think all types were weak against themselves, and that they all resisted the types they were super effective against, for example I assumed Water types would resist Ground attacks because Water is super effective against Ground.