I come from the software engineering background. My main problem with math materials online is how dense and unforgiving those usually are. I often read a math article and get what the author is trying to say, up until a certain point where I have no idea how they arrived from A to B. Sometimes I'm lucky and it clicks, but even then I think they could've been more empathetic to their reader and explain the same thing with multiple operations instead of combining them into a single one. It appears as if most of the authors think that their readers have the same context as they do.
I never have this kind of problem in software engineering. I can always find an answer to a question or a solution to a roadblock. In worst case I can run the code myself, debug it, see how it works, etc. You could probably do something similar in math, however sometimes it is not practical. Here's an example:
How did they arrive at this conclusion? The article is about Euclidean Algorithm, so why would I know about this property of numbers? If it's necessary to know this property, then how can I find the name of the property, so I could look around online for alternative and more accessible explanations? How can I verify it? Should I write a $200$-digit-number on paper to do that?
While writing this question I actually understood the first expression, but what if I didn't? A lot of times I just gave up on some problems because I couldn't wrap my head around it and didn't know how to find a solution or explanation, etc. I'd love to learn math but this process is super frustrating and breaks my motivation. How can I resolve those blockers on my own, so that I could be as fluent with it as I am with software engineering?