Cory Miller at Church Communications Pro has a very interesting take on designing logos.

...in his mind, he isn't thinking about your typical brand logo, like the classic Apple or Nike ones... what he's thinking about is a complicated family crest. The "logos" in this scenario are actually detailed stories, almost an essay, where it takes an hour for you to "hear" the whole story. Or "they're like one of those old 3-D wall paintings where you have to stare at it for 15 minutes before you actually see what's trying to be communicated there. That's the idea they have in their mind when you say, "Logo." I've lost hair because of this. Or... else that's the reason for the gray popping up.

This problem can be very difficult with logos, but I've seen this problem designing advertising too. The client wishes to portrait something in a much more complex way than is necessary, or even possible. There's nothing wrong with the story they wish to tell, they're often fascinating actually, but they are irrelevant to the purpose of the ad. The trick is to simplify the "story" into something which can be as simple as a feeling the ad can portrait. Read the whole post at Church Communications Pro, it's well worth it. Update: Church Communications Pro had a clarification in the comments that I thought was very important. In the post of his that I referred to, he was describing his solution to a "typical scenario" rather than a specific design theory. That might seem like a subtle difference to some, but it's actually quite significant. While I did understand his point correctly, I could have been clearer in my post.