Too many people take the path of least resistance and want to deliver quickly, because hey, who wants to spend time reading the docs, it's so boring. But that's just one of those things you have to do. The best programmers I worked with all share the thirst to go deep when they start using a library or framework. They spend a significant time reading the source code and the docs until they have a clear mental model how the thing works. The outcome of such approach is very few surprises when running the code, because the code behaves how you think it should behave.
My advice would be to mentor the dev of potential problems that would arise if you only partially understand how the library works. The most obvious are bugs or worse, you go against conventions and end up rewriting the whole app because it becomes unmaintainable.