A proverb meaning that the past is the past and one should stop dwelling on it and focus on the present (let bygones be bygones).
母はよく「昔は昔、今は今」と言って、過去のことをいつまでも悔やまないように私に諭した。
My mother often says, 'Let bygones be bygones,' advising me not to keep regretting the past.
あの失敗はもう仕方がない。昔は昔、今は今だから前に進もう。
That failure can't be helped now. The past is the past — let's move forward.
事情が変わったのだから、昔は昔、今は今で対応を変えた方がいい。
Since circumstances have changed, it's better to treat the past as the past and change how we respond now.