The pressure's on, but guess who ain't gonna crack?
Haha! - pardon me, I had to laugh at that

from Kanye West (Ft. Jay-Z) – Diamonds From Sierra Leone (Remix) Lyrics on Rap Genius

Since Jay has lost some friends and business partners, the responsibility of keeping Roc-A-Fella relevant is all on him, but he is ready for it

Pressure/crack is a reference to diamonds, which are created by high pressure conditions in the Earth and are extremely difficult to crack

Also, Jay could be laughing about the crack from his dealing days.

When he laughs, it could actually be a snipe at Fat Joe’s “Crack!” phrase in his music at the time. Fat Joe’s nickname was also “Joey Crack.” There was some small musical friction between the two.

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