Biff Loman

 
" The man don't know who we are! The man is gonna know! We never told the truth for ten minutes in this house!" Pg 104

This part is where things is clear as water for Biff. He realise what has been going on all these years. And from this quote we can tell that he is through. He is through with all these pretending and finally don't want to play this "pretending" game anymore. He wants his family to realise what he has learned. This show that he has been through certain amount of think and finally came up with solution. We can infer th at he become more mature and learn quickly, just by the "appointement" with Oliver.