A colloquial expression meaning 'anyone' or 'everybody', similar to '誰でも'; often used for emphasis or general statements.
誰だってそんなことは嫌に決まっている。
Anyone would certainly dislike that.
失敗するのは誰だって怖いものだが、挑戦は大事だ。
Everyone is afraid of failing, but taking on challenges is important.
誰だって最初は初心者だったんだから、焦らなくていい。
Everyone was a beginner at first, so there's no need to rush.