Proverb meaning that everyone has a past or background that influences their present actions and character.
彼の態度を見て驚いたが、話を聞くと納得した。人に歴史ありだ。
I was surprised by his attitude, but after hearing his story I understood. Everyone has a past.
あの人に対して厳しく言う前に、少し立ち止まって考えよう。人に歴史ありだ。
Before being harsh with that person, let's pause and think a bit. Everyone has a past.
失敗ばかりの履歴書を見ても、面接では『人に歴史あり』という視点も必要だ。
Even when seeing a CV full of failures, it's important in interviews to remember that everyone has a past.