Opportunity knocks but once.

良机难再。

《新英汉大辞典》

Opportunity knocks but once, so we must make the most of it.

机不可失，失不再来，所以一定要把握时机。

youdao

Opportunity knocks but once, so we must make the most of it.

机不可失，失不再来，所以一定要把握时机。

youdao