Hi, I think that expert is:

 A. Know many  tools in the field.
 B. Know how to use those tools.

Now the question of 'why/what/where/when' etc is that comes with the practicing expertness just like doctors and lawyers are 'practicing'.
What u have in mind about practicing beginner's mind? Remembering that tool itself is not useful, Usefuless lies in its functionality to get something useful to you. I would like to see 'usefulness' in your context.

Regards,
Artist