Truth be told, many clients don't understand this, either, and think that a logo or other communication piece is for themselves. They feel that if they like it, it must be good. These clients are the ones who would benefit from an arrangement with a market research firm.
The main reason I love the iterative process is that language is so subjective. When a client uses the words "flowing lines, shows that we provide personal service, high-tech but old-fashioned" what does that really mean? When I show a couple of samples of a design built from my understanding of those words, I get feedback which guides the next round.
I'm very good and fast at this. It's never "20 questions." Usually by the third or fourth round, the design is very close to what the client needs, and after seeing it, they realize it's what they would have described if they'd known exactly what they were after.