It’s hard to tell which error is important before you understand the issue well. I think if you understand the issue well then you can know what’s important. I think you can tell whats an error or not. You have to understand the issue well to know what’s important. What’s important tho? Errors? What else?
The quote says you have to learn. To learn something you gotta be able to tell what’s an error or not.
The quoted sentence starts with, “But.” That seems to mean it’s connected to the previous sentence. I think to understand an issue well, you have to learn about things you already don’t know well. You could tell what’s important when you understand an issue well, but you have to learn about things you dont understand well.