If you're lamenting the fact that you used to be able to shoot through a 500-page novel in like a day when you were in middle school and now you can't, it's worth bearing in mind that a big part of that is because when you were in middle school, your reading comprehension sucked. Yes, mental health and the stresses of adult life can definitely be factors, but it's also the case that reading is typically more effortful as an adult because you've learned to Ponder The Implications. The material isn't just skimming over the surface of your brain anymore, and some of the spoons you used to spend on maximising your daily page count are now spent on actually thinking about what you're reading!
Reading as a kid: "I can tell that this is supposed to be an emotionally moving ending, but I genuinely cannot remember who two-thirds of these characters are."
Reading as an adult: *reads a paragraph* *pauses* *reads the same paragraph again* *flips back and re-reads the preceding page to make sure you didn't misunderstand something* *stares into space for ten minutes as the Implications sink in*
added to this: most of us have a whole lot more going on in our lives as adults than we did as kids, in the sense of having a constant background awareness of Tasks That Need To Be Done, which impacts your ability to immerse yourself in a book. so whereas your middle school self could effortlessly devote their whole brain to reading, your adult brain is equivalent to an overtaxed CPU attempting to juggle thirty open tabs across two browsers, an excel spreadsheet, bloatware, security popups, the trial version of adobe, and a song that won't stop playing because itunes froze
