I found I wasn't asking good enough questions because I assumed I knew something. I would box them into a corner with a badly formed question, and they didn't know how to get out of it. Now, I let them take me through it step by step, and I listen.
I've fallen back on this periodically, although I must say that getting out of the grocery business ranked right up there with getting out of the army as one of the happier experiences of my life.