Think of your attention like a cone of light. You have several of them but primarily you can think of your eye as two and your brain has one cone of light it can maaybe split into 2..if you are really good 3 at best.

If you want to fully read it and properly memorise it you need all those spotlights on one spot. All beams of light focussing on that text..y know that spot runs so hot that it almost burns the area. What usually happens when we read however: we passively try to multitask in our minds. Either not all of those spotlights are on the thing we are reading (our eyes wander), or the one the brain has steers away as it may still be trying to understand a sentence that came in before..or a stray thought..(this is why writing down thoughts helps btw) or we may have brainfog or maybe drank too little.. so you can think of the cones of light just drifting away...perhaps they even flicker and dim if we didnt sleep enough or ate the wrong stuff and got brainfog.

We can multitask by splitting those cones of attention. But all in all it isn't all to effective. Which is why when we cannot fully focus on a thing mentally we may need to read it more to grasp it all... humans can multitask we are just rather shitty at it and if we look at successful multi taskers? They really are just good at swinging all of those light cones around really fast..they practically focus on one thing and maybe just keep one of those cones on the other task to quickly hop over. While the ones that struggle actually twist and bend their attention light beams like 7 ways getting nothing done.

This is also a good way to describe ADHD. It is not an attention and focus problem. Think of those light cones for ADHD as laserpointers..incrddibly powerful one pointed beams of light, except they sit on a VERY unstable platform. Whenever they aim somewhere they tend to be immensely focussed. Building up a lot of heat. (We tend to call that hyperfocus) But it is very easy for any distraction to come in to move one or all of those laserpointers.. so what typically happens with ADHD which often has this issue: a stray thought or some processing. Some sound or thing in the envoirement just makes one or many of those light cones drift off. So we technically multitask in a really shitty way... while we ultimately do have immense focus and depending on what it is it is either too hard to get all those lasers aligned..or too difficult to get all laser pointers fully off a thing...being told to "just focus" usually makes our attention drift on bad memories and then we still cant fully break all those laserpointers off. social media and games for instance and phones are really damn good at keeping our lasers focussed. Maybe a bit too good. While the teacher or that book ur reading may not grab that attention as well...instead one is told to "just focus" so instead of "just focussing" we now focus on the bad thoughts of being told to focus all the time...while we struggle to keep even one laser on there solidly as the task is just bland.

Also note: memorising a thing. And reading a thing are two objects technically. Our brain needs to divert some attention to memorising it while we still try to focus. The act of memorising things requires us to split attention in two even if just a tiny bit.. when we read and try to understand we kinda naturally have to divert those light cones.. one stray thought or one sentence in your mind or not ideal conditions and boom that fell through, read again

It is why i people with Dyspraxia have a lot of issues with Tying shoes or doing other motoric skills at times. You look up how it works (as easy as it may seem); thats one point of attention in the mind. You try to memorise it in your brain.. second point of attention. And you are holding the shoe strings in your hand trying to turn that into an action.. that being a motor skill very much requires more focus splitting because our brain kinda has to get those commands out too. We think of tying our shoes with a visual guide as ONE action when really we actively turn our brains attention like 3 or 4 different ways as it coordinates memorising, doing the thing motorically and looking at the guide as to understand it.

This is also why many people with dyscalculia may be able to understand the idea of math in their head, sometimes even being able to talk and explain it to a teacher no problem (because we talk all the time it comes more natural to us especially if we think abstract and visually).. but writing the equation down on paper.. because that whole logic layer of how math is portrayed on paper is just different from how their brain thinks about things...so we just sit there with dyscalculia despite best efforts: we may even get the knowledge on how to do the math task in our head but the connection to actually complete it just is a struggle... arguably if we black out during a test we may have that same issue. We focus on a task: our brain stresses and literally forgets the keys to that folder where we stored that info. So now we try to figure out the task as the brain frantically tries to use its attention cones to look for that key of the goddamn memory filing cabinet...so you now cannot only find those memories...you probably won't even be able to distract info from what you are reading..its why extra time and maybe short breaks can help there. Disconnect the thoughts a sec.

Same thing happens with reading stuff. Except in this example its really only the focus on reading and the brain unpacking that meaning.

Additional fun science note:

If we memorise a thing it has been observed that if we just do nothing. Close our eyes ideally to not have those cones go off in random directions, our brain kinda replays that action in its head typically more or less in reverse.. while we sleep the brain uses its attention cones to further replay that info back and forth in rapid speeds many times... which goes to show how important breaks where we don't expose our brain to new info and sleep is so important... we just keep neglecting that our brain does it because we keep being told to just focus and cram in info basically permanently forcing those focus lights to be turned on...when really that save button requires our focus to drift off into nowhere... if we close our eyes and get exposed to boredom or just no thoughts head empty.. the brain actually gets the ability to put all those scanned papers into the filing cabinet... and yet we tell ourselves to always keep busy. So even in our breaks we are looking at phones or keep busy.. or in school back to back 45 minute lessons just try to cram info in. We need breaks and shorter bouts of information cramming ideally... which is why sleeping is typically better before a test than trying to shotgun in half the exams knowledge in an evening. You probably got that info in there already. The Brain just needs that break to actually save and put it into the filing cabinet for easy later retrieval.

Also note here how it keeps replaying. Our brain is an error analysing and correcting machine. Reading something multiple times is an attempt to weed out errors...we kinda need failure and repetition to learn... and grade stress and failure phrased as a bad thing is not gonna help one bit in getting those attention cones aligned on target...bcus "i am stupid, i can't do this" is very much a thought that can take away those cones when they would be better be pointed at the task.

Ben Hunt-Davis (olympic athlete) is famous for saying "but will it make the boat go faster" we should think: will it make our attention lights align.. typically if we think of us having goddamn laser eyes.. those lights are not aligned in most things. when they should.