There are so many words in English (but also in Italian, for that matter) that can be interpreted either normatively or descriptively (e.g. “should” can mean either ‘is most likely to’ or ‘had better’, also “right”, etc.) that being unambiguous between the two is more exceptional than being ambiguous.
I guess the reason for that is that, for social norms, the two coincide, i.e. the side of the road on which someone in a given country had better drive is the one on which someone in that country are most likely to drive, the past tense of a verb one had better use in a given language in a given register is the one speakers of that language in that register are most likely to use, the attire you had better wear on a job interview is the one people usually wear on job interviews, etc.
There are so many words in English (but also in Italian, for that matter) that can be interpreted either normatively or descriptively (e.g. “should” can mean either ‘is most likely to’ or ‘had better’, also “right”, etc.) that being unambiguous between the two is more exceptional than being ambiguous.
I guess the reason for that is that, for social norms, the two coincide, i.e. the side of the road on which someone in a given country had better drive is the one on which someone in that country are most likely to drive, the past tense of a verb one had better use in a given language in a given register is the one speakers of that language in that register are most likely to use, the attire you had better wear on a job interview is the one people usually wear on job interviews, etc.