system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:What happens when you read but you don't register anything you just read?

(Also how do you FOCUS)
gpt
As you are reading this comment, multiple distinct things are happening, neurologically. First, your eyes are seeing these characters, and your brain is deciding how to interpret these data. Most people interpret words as a whole entity, not letter by letter. Once your brain recognizes a word, it makes the whole sentence, 'loads that sentence' into your short term memory. Then you decide how and or what to do with that sentence. If your brain interprets it as junk, (not what it's interested in right now), it just trashes it and moves on on to the next sentence. Sometimes this will happen with irrelevant details to the the larger thought. For example, 'the' is duplicated in the most recent sentence, and 'on' is duplicated in the previous sentence to that. Those small details don't matter to the entire thought, so your brain just ignores it. 

If you are thinking about other things and reading something boring, or you're tired... The same thing can happen. Your mind gets confused on what matters, and what doesn't so it makes some mistakes in processing. 

When you are FOCUSING, you're making a conscious effort that everything you are focusing on, is important. 

Make sense?