せいで

The grammar structure せいで is used to express that something negative happened because of a particular cause. It carries a strong nuance of blame or fault, indicating that the cause led to an undesirable or unfortunate result. This distinguishes it from おかげで, which is used when the result is positive or favorable.

Structure

• Verb (plain form)
  • せいで:
    ねぼう寝坊したせいで、でんしゃ電車にのりおくれた乗り遅れた。

    Because I overslept, I missed the train.
• い-adjective
  • せいで:
    みち道がくらい暗いせいで、ころんでしまった転んでしまった。

    Because the road was dark, I tripped and fell.
• な-adjective + な
  • せいで:
    ふくざつ複雑なせいで、だれ誰もりかい理解できなかった。

    Because it was complicated, nobody could understand it.
• Noun + の
  • せいで:
    たいふう台風のせいで、ひこうき飛行機がけっこう欠航になった。

    Because of the typhoon, the flight was cancelled.

せいで vs. せいか

When the speaker is not entirely sure whether something is the cause, せいか (perhaps because of) is used instead. It softens the blame and adds uncertainty.

～せいにする – to blame

The expression 〜～せいにする means "to blame something/someone".

Important nuance

Because せいで implies blame, using it about someone's actions to their face can sound accusatory or rude. For neutral cause-and-effect without blame, structures like 〜～ために or 〜～で are more appropriate.