Lennie asks George to tell him about their dream. The dream is to get their own ranch, raise their own animals, live off the fat of the land, and make their own money. This dream is important towards the development of the story. The entire time, the two want to get their own home and live on their own. It plays as their motivation factor, and would later be demolished and a failure. This dream follows the theme of central idea, as this dream is what the two are after throughout the novel.
You hadda do it.
Curley gets into a fight with Lennie. Lennie is being beaten bad, and it isn't until George demands him where Lennie would fight back. He grabs Curley's hand and breaks it in his own grip, ending the fight. This scene somewhat shows Lennie's lack of control for his own well-being. He needs the demand from George to fight back, and without him, he may of been beat senseless. This scene shows the theme of conflict of character. Outside of conflict between characters, Lennie has serious mental issues where he doesn't understand his own strength and overall common sense. This lack of understanding his own strength will later take part in chapter 5.
Curley's wife is found dead by Candy and George. She was killed by Lennie. she had invited him to feel her hair because it is soft. Lennie would then make her panic. He accidentally snaps her neck trying to cover her mouth and prevent her from screaming. Candy asks if their dream is dead, and George replies it is. A lynch mob is formed, and they go after Lennie. Relaying back towards the theme in chapter 3-4, Lennie doesn't know how strong he really is. Him murdering Curley's wife marked the end of their dream and any chance for the two to have a good future together. The theme of failure and acceptance plays part into here. The failure aspect comes from the reality of the situation; Lennie committed murder, and he will soon fall to the same fate. George accepts what will become of Lennie and that their dream is dead. This acceptance of Lennie's shines in chapter 6.
Lennie retreats back to the river area where George says to meet up if he's in trouble. George meets with him here with an angry mob approaching. The two talk about their dream again. George tells Lennie to look out into the river and try to picture their dream. While Lennie is distracted, George shoots Lennie in the back of the head. Not long after, Slim and others meet up to find a dead Lennie and a devastated George. Slim talks to George, telling him he "hadda do it." George decided to kill Lennie himself and not from the lynch mob. George most likely didn't want Lennie to suffer from a lynch mob, or maybe it would only be fair to Lennie for him to die only by the hands of George. Slim put it wise however; George had to do it. The dream died with Curley's wife, and George had finally accepted it. Acceptance plays another major theme here, but so does resolution. In every aspect, Lennie was a liability. George had said how he could do so much more if it weren't for Lennie. Lennie's death marked the the acceptance of the dead dream, but also the beginning of freedom for George. Setting this in stone for both the dead dream and freedom, Slim and George end by going to get a drink.