When I started teaching English as a foreign language to gifted Korean high school students, I sometimes struggled to explain the why behind a correction. It was easy enough to explain some rules, even ones that challenged native speakers, such as using "less" with mass nouns and "fewer" with count nouns.
But why were verb forms like "going to" and "will" (as in "he's going to call them" and "he will call them") often interchangeable, but sometimes not? And why did it sound so wrong to say "the yellow big bus" instead of "the big yellow bus"?
My students were curious, and I wanted to give them concrete explanations. The problem was, not only did I not know the rules, I often didn't even know what to look up. What do you call words like "thankfully" and "hopefully" when they apply to the whole sentence instead of just the grammatical subject? If you don't know the term "disjunct adverb," it's tough to look up the rules governing their use.
Every day, I learned more. And after two years of teaching, I could explain a whole lot without looking it up. Even better, I'd found the resources to check anything I hadn't yet learned.
Now, when I need to check on a particular rule, I almost always know what I'm looking for. I can google "exceptions to rules on hyphenating phrasal adjectives" or look up "disjunct adverbs" in the Chicago Manual of Style's index.
It's a lot easier to find a needle in a haystack if you have a magnet.