What are the mistakes committed by players who take many years to become an expert? I am a beginner and am targeting to become an expert. I see many people who barely takes 4 years to become an expert and many people who take 10 years to become an expert. I don't want to repeat the mistakes committed by players who had slow progress. What are the mistakes committed by players with slow progress? Some of them that I could think of are 1) lack of reading books  2) lack of proper coaching  3) merely playing thousands of games without strategic development. What do you think? Can you please provide suggestions on how to be efficient in my preparation? What is the best way to train?
I can think of three mistakes that a lot of class players who think they're working on their chess make:


They read chess books.


In particular they buy lots of them and then skim them, or study / try to memorize them as if they were textbooks.

Most low level players don't take the time to really get to the bottom of the positions in the books, they don't work with them, only passive consumption.


They memorize openings.


Opening books sell far better than all other types of chess book combined, even though the best they have to offer a class player is a slightly better position against someone who else who had memorized the opening but not quite as far. It's fun to feel like you're playing as a grandmaster, and sure it will lead to some short term improvement, but in the long term this is mostly wasted time.


They don't analyze.


What class player is actually able to take any position and start analyzing it to figure out what's going on? Not many, even though that's what the actual game is about. The best way to improve is just analyze a lot of positions, especially together with a mate (so you can argue and learn from each other), especially your own games. But few put in the work.

I know this because I'm very guilty of all three.