Used to give a reason, express cause or bring up a topic; 'because', 'since', 'it's just that'.
The A。だって B。grammar point is used to give a reason, express cause, or introduce a topic in a casual manner. It can be translated as 'because', 'since', or 'it's just that'. A is the reason and B is the statement that follows due to the reason. It can be used with verbs, い-adjectives, な-adjectives, and nouns.