@Baysiri
It's not his fault, though. He was very literally brainwashed to think the way he does. He had lies and falsehoods drilled into him
literally his entire life until he was conditioned to genuinely believe everything his parents told him was the truth. He's never had any other frame of reference towards anything they've ever told him, and because of the manner at which they brainwashed him, he takes every word they say as absolute fact. Therefore if his parents say "everyone in the outside world is stronger than you" or something to that effect, naturally he's going to assume anyone who doesn't appear stronger than him is simply holding back for his benefit.
Everyone says he's naive or stupid or dense, but there's a lot more to it than just that. Brainwashing of that nature isn't something you can simply get rid of so easily. Again, he's never had any other frame of reference to anything, so naturally reality will take a lot longer to sink in. He was raised to believe his parents words with absolute faith.