_That's_ it.

I don't think you can possibly see it, but that is the main trouble.
"That, too, brings me to my next point, and this I find harder still to express.

I want you to realise that I feel as if I had never seen life before.

I feel as if I had been shown all my days a certain number of pictures and told that they were the real thing, or given certain descriptions and told that they were true.

I had always accepted that they were.