He figured that most if not all of them would have major psychological problems. Maybe even go completely nutso. (1.14)
This seems to be one of the central ethical issues surrounding the whole WICKED experiment: even if the kids do emerge safe and victorious, they're all going to be pretty messed up as a result of all of the trauma they've experienced.
He was actually trying to decide whether he was more confused or scared when a clanging bell began ringing throughout the room. (7.1)
The amount of suffering these kids go through actually messes with their emotions, causing them to be confused in situations in which their instincts should tell them, Hey, you should be scared right now, or Hey, you should be excited right now.
He suddenly thought of Chuck and what he might say if he were there.
Something simple, probably. Something like, this sucks.
You'd be right, Chuck, Thomas thought. The whole world sucks. (11.5)
The whole world sucks. Hmm, that's a pretty nice outlook—but how can you blame Thomas for thinking so? Is there anything good about the world he's been placed into?
Getting his hopes up was something he'd sworn never to do again. Not until all this was over. (15.31)
Here is another example of how Thomas is truly put through horrible circumstances. Hope can sometimes be the one force that can keep someone going; without hope, giving up seems like a pretty viable option. What does Thomas hope for?
He sobbed, surely from the pain, probably also from the trauma of what he'd just been through. (16.20)
Traumatic suffering can be worse than physical suffering—just ask Winston, whose head was attacked by a gigantic silver blob.
He'd just killed a man. He'd taken the life of another person. His insides felt full of poison. (34.4)
Sometimes suffering doesn't always happen to the person who is harmed; it can also happen to the person who is doing the harming. Thomas is super traumatized when he kills Mr. Nose, and we have a feeling that'll haunt him for some time.
Too much. It was all too much. (43.25)
That's a pretty accurate way to sum everything up for the Gladers. Thanks, Thomas, for the insight.
The image of the sick boy, Ben, being Banished back in the Glade swam back into his brain. An odd time to think it, but now he knew how that kid had felt in those last seconds..." (51.37)
Thomas thinks about Ben right while he himself is being closed off by Teresa and Aris. Understanding someone else's suffering—in this case knowing Ben's—is a direct path to feeling empathy.
Though he certainly didn't think of himself this way, he and the others were just kids. Kids! (54.11)
Yeah, we should probably keep in mind that all of this suffering is being experienced by kids. It's one thing for a bunch of grown adults to be suffering through WICKED's trials, but these are just kids—their brains haven't fully developed, and their lives haven't really been lived yet.
"If we haven't done enough to pass your stupid tests, then we fail. The tests are over." (62.4)
Thomas feels like everyone's suffering has gone too far, so he can't bear to see more death. He says this to a WICKED officer, pretty much demanding that he not kill Brenda.