せいだ

it's ...'s fault

→ せい
phrase Very common #1,512
it's ...'s fault Often follows の to blame someone or something for a negative result.
JA: 雨のせいだ。
EN: It's because of the rain.

マネージャーは失敗は自分のせいだといった。

The manager said the failure was their fault.

多分、今日トムが来てないのはそのせいだ。

That's probably why Tom isn't here today.

俺が⸺バカな夢見たせいだ

It's because I had a stupid dream.

— Godzilla Minus One (2023)

それはまるで、その惨事が彼のせいだとでも言っているような物だ。

It was almost as if to say that the disaster was his fault.

"環境が変わったせいだ"

It’s because the environment changed.

— 箪笥<たんす> (2003)

彼は自分の成功は努力したせいだと言った。

He said that his success was due to his hard work.

一緒だった私が必要だと…私は二度と会わないと…私のせいだ

That I, who was with you, was needed… That I’d never see you again… It’s my fault.

— オッペンハイマー (2023)

集会を召集したのはマクサンスに酷いことをしたせいだ

The meeting was called because something terrible had been done to Maxence.

— コーラス (2004)

下痢もそのせいだ

The diarrhea is because of that, too.

— 火垂るの墓 (1988)

環境が変わったせいだ

It's because the environment changed.

— 箪笥<たんす> (2003)

お前のせいだ!

It's all your fault!

— ANORA アノーラ (2024)