别为你的错误担心；毕竟这是你第一天。

Don't worry about your mistakes; ___after ___all, it's your first day.

我们当然和好了——毕竟我们是最好的朋友。

Of course we made up - ___after ___all, we're best friends.

他累了并不奇怪——毕竟他工作了一整晚。

It's not surprising he's tired - ___after ___all, he worked all night.