I'm not a native speaker so this may be obvious to some of you. I've come across the figure of speech "to break the mould", basically meaning to do your own thing and not adhere to traditions or rules, which may or may not be obsolete. Every time I came across that phrase it was used in a positive context, rebellious maybe, but positive nonetheless.
While I get why it could be seen as a positive character trait to have your own head and not mindlessly follow everything you're told, I don't understand why this particular figure of speech would be positively connoted.
From what I understand it comes from industrial casting, where every cast part comes from the same mould so they're all the same. If one part would break such a mould, not only would it be way out of shape and unusable for any further purpose, it would probably also cause considerable damage and delays in the entire manufacturing process. Neither of those outcomes seems desirable to me in any literal or figurative sense.
Does anyone have some insight into that?