The climax of any story gives the reader an idea of which way it might end. It represents a turning point and the reader is in a position to consider the possible outcomes. In Of Mice and Men, John Steinbeck's characterization of Lennie and George prepares the reader for the outcome. Through their actions, the reader has no doubt of their commitment to each other and to their dream. The reader is also aware that this story could end tragically due to the foreshadowing as George must fix each of Lennie's indiscretions.
George will protect Lennie at all costs and, even though he is overwhelmed and resentful sometimes when Lennie "done it again," he knows he is duty-bound to protect him from himself. The climax comes when Lennie kills Curley's wife and runs off to hide where he knows he will be safe. He knows George will make things right. George will do anything for Lennie and has always minimized the consequences of Lennie's actions, from his dead mouse to his puppy and his inappropriate behavior.
Lennie has some sense of George's feelings although he can neither understand nor explain them. This is something George cannot fix and so it changes the possible outcome as George has run out of choices and can only protect his friend from himself by killing him, destroying any chance for either of them for the future they so wished for. Both men must face the reality and the fact that their dream will never be realized.
In "Of Mice and Men," I would say the climax of the novel is when Lennie accidentally kills Curley's wife. This is the climax because this caused the greatest change in the book. Before this, George and Lennie were living a peaceful working life on the farm, and still had the dream of one day owning their own farm. After this event occurs, George realizes that he can no longer protect Lennie from his mistakes and that dream can no longer be possible with Lennie, because Lennie is going to die either by George's hands or Curley's. This caused George to make a great decision that changed their lives drastically.
The climax is the turning point of a novel. In Of Mice and Men, it is most commonly said that the climax is where Lennie kills Curley's wife because it foreshadows that when everyone finds out George will protect Lennie from harm. However, I would say the climax is when George Kills Lennie because it is "the most intense... important point..." which is the dictionary definition of the climax. It is the part of the story where the author's main points about the novel are shown and it is the most intense part of the novel.
I would say the climax is when George realizes that he cannot protect Lennie any longer as this is an intense decision on George's part to give up their common dream and to kill Lennie instead of letting Curley kill him.