I've been reading Albert Einstein's biography, and something struck me today about him. He made these amazing leaps of imagination, but one of the things he was particularly good at was explaining incredibly complex concepts to normal, non-scientists. Today I was reading about his postulates concerning the speed of light and his special theory of relativity, and his explanation of it involved nothing more than a scene with two people, two lightning strikes and a train. This is to explain a couple of the most complex scientific theories.
A month or so ago, I was talking to a director I was working with about how much of our job is articulating our ideas. Yes, coming up with great ideas is important, but a great idea poorly communicated is dirt. Your job when you present to your client, or present to your creative director, or explain your idea to a director--heck, even when you explain it to your partner--is to articulate your idea in such a way that they can see in their head exactly what you see in your head.
This quarter, I'm teaching a scriptwriting class. The first assignment I gave was to take a commercial they like and write the script for it. Just watch the spot, then write what they see. Then I had them present the spot to us in class. After they presented it, we watched the spot and critiqued them on their presentation. Did what we saw on the screen match what we'd imagined when they presented it? If not, how was it different?
This isn't to say than an execution won't change from the time you think of it an the time it's finished. You should be open to creative input from others--directors, actors, etc. The point is that your presentation, your articulation of the idea, is incredibly important. If you're specific and clear, you shouldn't run into a client seeing the final project and saying, "That's not how I pictured it." You hopefully won't ever come to a set and look at the art direction and say, "Oh shit. This is completely wrong." It's not always an easy thing to do. But we're in the business of communication. So make sure you're communicating.