Throughout the history of the written word, there has been one topic that appears in each of the stories. Usually, it pops its ugly head in during the latter half of said tale. It is the climax. The climax is the conclusion to the plot. And, the climax is also usually consisting of the main character making a hard decision. This decision is most always a bit difficult from the character's standpoint, hence the title "Hard Decisions." In Steinbecks Novella of Mice and Men, that criteria falls on the main character, George.
In the novella, George was traveling with a rather large and not-so-bright man, Lennie. You didn't know why they were traveling, but that fact doesn't matter until later. What did matter at the beginning is that they were looking for work, but also trying to hide at the same time. Then the chance for both struck. They ran across a small ranch, and found the opportunity to make some money, and live in solitude from big cities. But, problems arose. The owners son, Curly, tried to raise trouble with the other workers, including Lennie and George. The taunting led to a couple of bad events, one of which was Lennie breaking Curly's hand. That wasn't so good, because Curly was a pretty good boxer, and was trying to make a living about it. From then on, things didn't go so well.
At another point in the story, a different worker, Slim, has to make a hard decision. His dog was suffering from age, and he had to do something about it. After a bit of listening, he let another worker take the dog out an put it to sleep. Did this scenario reflect another one? The dog was disabled. Lennie was [mentally] disabled. That seems to be a pattern. George eventually saw that Lennie living like he did was similar to Slim's dog. He thought that letting Lennie go on longer may put more suffering on him like it did unto the dog.
The final straw came near the end of the story. Lennie had again gotten himself into trouble, but this time it was serious.