Does "cannot be" mean similar thing to "must not be?" What's the difference?

Native speaker’s answer

Rebecca

It's kinda similar, yeah! The difference is that "cannot be" implies that it's important and that the process can't happen or is impossible if this thing isn't done. "Must not be" implies that there is an option, but you aren't allowed to do that thing. Ex: You must not be so harsh on yourself. => not allowed to = You cannot be so harsh on yourself. => shouldn't be possible Ex: The cakes cannot be over-baked. => perhaps there is a consequence that follows. = The cakes must not be over-baked. => not allowed to be

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