Certainly this applies when you don't fully understand him, or when you disagree. But even if you agree with him, don't think that you've gotten the full message. Even when something seems obvious to you, try viewing it in a different light. Many times, to your surprise, you'll see new aspects that you previously overlooked. We don't completely understand an idea for a very long time.
Wisdom is very deep.
We may think we immediately understand, but as time passes, we accumulate more life experiences, and begin to unravel the layers beneath the words. There are a thousand different aspects you haven't thought of. So you've got to keep digging. Get into his wavelength. Figure out where he is coming from.