GRAMMAR DETAIL

のだ

the fact is that · it is because

Adds background or an explanation to help the listener understand the preceding situation.

Examples

道路がぬれている。さっき雨が降ったのだ。

The road is wet. The fact is that it rained a little while ago.

電車が遅れているので、会議に間に合わないのだ。

The train is delayed, which is why I will not make it to the meeting on time.

Structure: のだ presents the preceding content as an explanation of a situation and is also shortened to んだ in speech.
Basic usage: 道路がぬれている。さっき雨が降ったのだ。 makes sense of the wet road by connecting it to earlier rain.

Explanation added to a fact
- 雨が降った can report the fact that it rained, while 雨が降ったのだ presents that fact as an explanation in the current context. It links the statement to a situation rather than simply making every sentence more polite.
Present affirmative connections
- Nouns and na-adjectives insert な, as in 休みなのだ and 静かなのだ. A verb connects as in 休むのだ, so distinguish the noun 休み from the verb 休む.