There were these things inside the maze. We called them Grievers. They were huge, half kind of machine, half...I don't know what exactly. Giant spiders, maybe? They used to stay inside the maze. But the doors stopped closing at night and they came out. They were attacking.

If we hadn't gotten out, they would've killed everyone.

[That was the trigger. The motivation to get out. He had it without that, but so many of the others had been okay with just staying in the Glade, like Gally.]