わけ

The word わけ, which generally means "reason", can be used in a few scenarios. First, the speaker can use it to provide a reason for a statement they've made. Second, the speaker can use it when they've reached a logical conclusion based on what they've just learned. Third, the speaker can use it when expressing they understand the reason behind something they've just heard or discovered.

あっ、ヒーターが止まっている。寒いわけだ。
Ah, the heater is stopped. No wonder it's cold.

Ａ：スミスさんは日本に２０年も住んでいたんですよ。
Ｂ：なるほど、それで日本語がとても上手なわけですね。
A: Smith-san has lived in Japan for 20 years.
B: Ah, so that's why his Japanese is so good.

東京は電車や地下鉄やバスが便利な街なので、車がなくても生活できるというわけです。
Tokyo is a convenient city with trains, subway, and buses, so that's why they say that you can live there even if you don't have a car.

先週リーさんのお母さんが亡くなってしまった。今朝は話さなかったわけだね。
Lee-san's mom passed away last week. So that's why he didn't talk this morning.