expression
not necessarily; not always; there is no guarantee that
Used after a clause to indicate that something is not always the case or cannot be taken for granted. Often follows からといって or a plain-form predicate.
高いものが必ずしも良いとは限らない。
Expensive things are not necessarily good.
日本人だからといって、寿司が好きだとは限らない。
Just because someone is Japanese doesn't mean they like sushi.