LOL
I will bold what I have learned that sticks with me.
Most of what I know was taught to me by people who beat me, second guessing after, stealing things.
2nd is watching games, but
looking for specific things, getting questions. For example I am looking now at how NBA teams trail through ball screens, rather than fight over. I don't like it, but I am probably wrong, since high level guys ar doing it. I just don't know exactly why.
Never be scared to admit I don't understand something. As a highschool coach I shred zomes now, but that was because it used to be my worst thing. I wasted probably whole seasons whinging about jerks scared to play man ot man.
Most I learned from experience But,
there are some really good young coaches who to paraphrase Cosell "never played the game" who l
earn from clinics, and youtube. There are alot of good things online. At one time I coached with NCAA rules so NCAA guys were my models, now in FIBA is close to NBA, but the talent of NBA guys does not transfer to high school. I like WNBA sets to be honest since they use NBA stuff sans the alley oop.
I would say pick something and learn way too much about it. If it was history reading five books about something you maybe start to get it, right? I would start at a tactical level "defending the ball screen." But watch lots, old and new. Lots of coaches will be what I now call Mandalorians "this is the way" who will say there is one tactic, or one approach, but if you watch lots you will see some common ideas, but also opposite approaches. The good stuff will explain which talents fits which tactic. Then watch games. Stuff will jump out at you, you may see "Okay Brown is trying to do ________" or "What is Kemba doing?" Then look at the offence.
Always study, always teach both sides of the ball. Dean Smith said he developed his "force baseline" because all his O sets were about getting the ball into the middle. Shouldn't the D be the opposite?
If you really want to just understand your favorite team look up "Celtic Breakdowns" etc.
Personalities, wow. That is a harder one. I really like reading anything by Bill Russell about winning, Hubie Brown was the best presenter about this I ever saw, since he talked about people overrating one idea. Lots of stars Jordan, Bird, KG are visibly angry while they play, but Duncan, Kareem, Kawhi, are subdued. Just from books 1950s writers loved the relaxed, cool winner, so loved Dimaggio, Mantle, Mays, and the intense guys like Ted, Bob Gibson, were appreciated more by later generations.
Hope this helps.
EDIT
I will plug this guy I know, a Canadian guy that has a pretty good site/youtube channel
https://www.youtube.com/channel/UCBBw1Rq6lxyoTgFxcChiq8Q