You up so late, the motherfuckin bar closed
But you need a drink "why you work so hard bro?"
Its for moments like this!

from Big Sean – Funkmaster Flex Freestyle 8/13/13 Lyrics on Rap Genius

Meaning

Bars usually close in the early hours of the morning— 2-3 AM. Sean was up passed that working to the point he needed a drink for relief, but he couldn’t even get one. He’s asked what does he works so hard far?

It’s for moments like this:

Being able to compete and work with his idols, rock shows, and all the other perks of living out his dreams.

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