命運無常。

Eminem put it right in the song:

This opportunity comes once in a lifetime, yo
You better lose yourself in the music
The moment, you own it, you better never let it go (Go)
You only get one shot, do not miss your chance to blow
This opportunity comes once in a lifetime, yo
You better

人生也是如此：一個人， 一個機會； 一扇窗， 一個世界。