Manny says he doesn't know how he screwed up. He could have done nothing true, but as in, he did nothing with his life. He seems the drab and beaten down type at the beginning, maybe that's what he was like in life??
Manny:"Well, when it comes to shreds, Dom is the expert."
Hector:"And by the same logic Manny, you're about to become an expert in botany."