Out of all of the original 100 kids sent to the ground, Monty is the one with arguably the strongest and most consistent sense of morality. He is constantly trying to do what is right.
In the trailer for "A Lie Guarded," Jasper angrily tells Clarke that she isn't God after finding her list of the 100 people who will live in Alpha Station. With all these lives in her hands, what decision will Clarke make?
On "The Four Horsemen," Clarke made the difficult decision of listing the 100 people who will live on Alpha Station if she's not able to come up with a better solution. Clearly, that's weighing heavily on her.