expression
as if it were one's own affair; as if it were about oneself
Used when someone empathizes deeply or gets involved in another's matter as if it were their own. Often followed by verbs like 喜ぶ, 悲しむ, 心配する, 怒る.
彼は友達の成功を自分のことのように喜んだ。
He rejoiced at his friend's success as if it were his own.
彼女は私の失敗を自分のことのように心配してくれた。
She worried about my failure as if it were her own.
Phrase composed of 自分 (oneself) + の (possessive) + こと (matter) + の (nominalizer) + よう (appearance/manner) + に (adverbial). Literally 'in the manner of one's own matter'.