After the events of the previous night where the grievers invaded the clearing, the group decides to risk everything and escape the maze, but Gally refuses, most of the other Gladers are at the door, trying to convince the others to leave with them, and you try convince Gally, but he's stubborn and you know deep down he's just scared.

"Good luck with the grievers"

He says as a final word, implying that he's not going to leave, but you won't give up on him that easy