articulation.

a lot of designers have trouble with it. i sure as hell did. they don't really teach you this in design school. yes, it's easy to respond in a kind-of "this is why i used this certain type / color / grid / etc" when you're designing more pragmatic materials (bus cards, letterhead, brochures, etc)... but those kind of quantifiable decisions are less obvious when it comes to new media design work. if you do work that involves motion, interface design, or that involves support from other media (like music), a lot of these decisions become more esoteric, but make sense at a gut level if you're worth anything in this game.

the fact is, a lot of clients want really tangible decisions. be creative. you'll come up with something, and i bet it'll make sense. because it probably already does make sense; that's why they're paying you. learning the marketing lexicon will help a bit. they need to trust you. being confident will sell the idea more than you think. just my two cents, which now that i think about it, you should avoid at all costs. in fact, forget you read this.