I often talk about a type of pattern recognition with this sort of stuff. Over time you start to develop a sort of automatic pattern recognition skill that sep

I often talk about a type of pattern recognition with this sort of stuff. Over time you start to develop a sort of automatic pattern recognition skill that separates problems to "I've never seen this before" and "oh, this looks very similar to x". Also it becomes much easier to know what's hard and what's easy, like you said. You still obviously make the wrong call here and there. More often if you're in a completely new field, like the OP.