"Those that don't buld, Burn"

When Faber says "Those that don't build, burn" he means those who don't grow and learn from tough situations, will just make their lives worse. If you don't try and correct the wrong that you see going on and you don't try and fix your mistakes you will just make society and life worse and you will be "burning" it. That's like our society and like how society has always been because their are always people that have the ability to correct a mistake or grow from a bad situation and they don't because they wallow in their own self-pity. In Fahrenheit 451 Faber admits to Montag that he saw the society going downhill and he didn't do anything about it. I think that he feels like he burned the society and feels guilty about it and he is trying to make up for it with Montag. He doesn't want Montag to make the same mistakes that he did.