I'm just going to elaborate on what you didn't understand, meanwhile I'll check out the guide you suggested to me
so I pick a player, watch their videos. slow it down, pause alot, rewind and rewatch. Ask yourself questions about why they made the choices they did, and try to answer them.
so I'm going to watch the videos in the mind set of learning guaranteed followups, setups, or combos. But something that seem guaranteed (even in friendlies or solo lab) might not be guaranteed because the person has insufficient knowledge or had 4 frames to jump away or to avoid the supposedly guarantee hit. so how do you deal with that?
also when I pause and this person chose a move that send X to a place where it's to far for a followup or a tech chase, how do I know the the optimal option in this situation to fit this quote? "when you touch him, you want to make sure he dies"
https://www.youtube.com/results?search_query=marth+movement&spfreload=10 i watch this video and they are doing raw fsmashes everywhere. I know that this is fundamentally wrong with marth because quote iirc "if you can get a guaranteed fsmash with marth, chances are you can deal more damage choosing other options"
but having watched a lot of high level marth players I still couldn't figure out what the optimal move that I could do to in place of that fsmash nor I can figure how this player can even play fundamentally proper in this case
all I know is that their dash dance is just random dash dance and that their positioning isn't even positioning