An expression of consolation meaning 'there's always tomorrow' — if today goes badly, you can try again tomorrow.
今日は失敗したけれど、明日という日もあるから、また挑戦しよう。
I failed today, but there's always tomorrow, so I'll try again.
落ち込まないで。明日という日もあるよ。
Don't be down. There's always tomorrow.
忙しくて疲れた日は、無理せず休もう。明日という日もあるしね。
On tiring, busy days, don't push yourself — rest. There's always tomorrow.