Do you ask him to justify right on the spot though? It takes time for me to sort through my thoughts on something and revalidate it. In big discussions, I like keeping around a piece of paper to get my ideas down well. In a few seconds, he will be able only to tell you his overall big judgement. On a given issue, I have almost a mental outline of my thoughts. A bullet point list, if you will. With lots of subheadings and such.