George and Lennie are both sitting by the fire eating beans and talking. They have a dream of owning their own farm with livestock and crops. Their dream is symbolic of the American dream. While the snake slithering by represents the bad things that will happen along the way. This dream that they have will be filled with many obstacles for which they will need to overcome if they want to reach their end goal
Let's do it now...
Carlson takes Candy's dog into the woods and shoots it. Candy's while looking back at situation says " I ought to have shot that dog myself". Candy wasn't planning on his dog being shot and wasn't prepared for it to happen.
Lennie accidentally snaps Curley's wife's neck and quickly realizes mistake. Lennie has ruined his chances of accomplishing his dream because of this. The person can ruin their own chances of accomplishing the dream they have.
George is forced to kill Lennie after Lennie killed Curley's wife. George and Lennie's dream is no longer reachable by the end of the story. This is down to them and they are solely responsible for not reaching their goal. The american dream is mostly unattainable by the dreamer themselves