Expresses that something is not necessarily true; 'not always', 'not necessarily'.
Verb-casual + とは限らない, い-Adjective + とは限らない, な-Adjective + だとは限らない, Noun + だとは限らない
Long explanation:
The ~とは限らない grammar point is used to express that something is not necessarily true or does not always occur. It can be translated as 'not always' or 'not necessarily' in English. The formation differs depending on whether it is used with a verb, い-adjective, な-adjective, or noun.