Quote 19
Before I didn't even know to be mad that we can't open Door, my head was too small to have Outside in it. When I was a little kid I thought like a little kid, but now I'm five I know everything. (3.20)
The more knowledge Jack gets, the more he thinks he knows everything. He doesn't yet have the knowledge to know that he will never know everything.
Quote 20
"I don't want there to be bad stories and me not know them." (4.1051)
Jack wants to know everything, and we mean everything, even if it makes him feel uncomfortable, scared, or weird. That's pretty ambitious for someone of any age.
"I'll get bigger and bigger and bigger till I turn into a human." "Actually, you're a human already," says Ma. "Human's what we both are." I thought the word for us was real. (1.133-1.135)
Jack might understand a lot of words, but being trapped inside Room limits his ability to understand some of them. He thinks that he and Ma are the only "real" people and that everyone else, even the humans, inside the television are not real. It takes him a while to grasp this concept.