Maybe you just didn't really see it. I've begun to notice that I don't even see certain things that I read, especially if I'm not intellectually prepared to receive them. I vaguely remembered the mice and the earth being a computer (once prompted by the post), but I had no idea about the mice being 3D projections of a multi-dimensional being. I'm pretty sure that idea was either not something I truly comprehended at 20 and/or I thought it was stupid/random (my opinion on the book as a whole), so the thought never even sank in.

Other times I just don't see something for other reasons. I read Augustine's Confessions and never saw the famous line "our hearts are restless until they find their rest in Thee", which is in the THIRD sentence! I'm not sure if the antiquated English [1] threw me off, or what. In fact, I don't remember seeing pretty much every quote people take from Confessions, besides the pear episode. Some of those are theological ideas that are just completely new, some are probably my annoyance at his "confessing" things that aren't really faults [2], and my annoyance at his insistence on quoting the Bible everywhere he could [3]. But I find it strange that I seemed to have simply not seen most of what other people get out of it.

[1] Rant: don't bother reading the out of copyright translations of ancient works, because the 1800s and early 1900s seemed to think that because the works are old, it should be translated into old English. This is stupid. Augustine didn't write in 500 year old Latin, so translating it into 500 year old English is mistranslation.

[2] I am starting to think that maybe "confess" might have meant something different, and it is not confessing a faults but a statement of beliefs.

[3] I suspect that ancient ideas of rhetoric valued quoting trusted sources a lot, kind of how classical Chinese literature quotes older classic literature a lot. Augustine, being a professional rhetorician, would in that case be expected to do that. But it drove me nuts.