I think the ease with which your IDE lets you get and debug into the source code of your dependencies (assuming your language lets you do this) is definitely so

I think the ease with which your IDE lets you get and debug into the source code of your dependencies (assuming your language lets you do this) is definitely something I overlooked in my earlier development career as pivotal to better understanding not only the dependencies, but how to think about software from other peoples' POV, which when done often enough gives you a better intuition for where and why different bugs manifest. JetBrains indeed makes some awesome products.