WHAT ARE YOU THINKING ABOUT RIGHT NOW?

Dreams: It's true archetypes will be different from person to person, which is why the only best interpreter of a dream is the person who had it in the first place, but there are certain consistent things that mean essentially the same thing to people. Archetype is probably a better word than metaphor (metaphors are more generalized). It's true, you could dream about getting your dream car for your birthday, but then in that case, it would represent the best of you. That's the whole point; you wouldn't even be dreaming about it unless it meant something to you.

Most people own a car in the modern age. Most people who own a car depend on it for their very livelihood and for many people, the loss of that essential transportation for an extended period of time would be ruinous. I could just imagine taking a bus to tune a piano: half the tools I need (and spools of string in case I need to replace any) would probably get me arrested. Most people don't take care of their pianos, and as frustrating as can be sometimes, tuning a piano is rarely just tuning a piano (felt is coming off of keys, springs are breaking or knocked out of position, old glue has dried and pieces are coming loose: I carry a selection of tools with me just to assure the piano even can be tuned. You can't tune it if it won't play.).

When you go to get groceries, you drive. You drive to visit your family. You drive to and from work. You drive your kids to and from school, little league games, science fairs, the zoo, the amusement park, football practice. Naturally, people associate it with their most basic needs, and when your dream features a car, what the car's doing in the dream almost always reflects your behavior and actions in waking life, and that's specifically because it's so tied to your life. 200 years ago, it would have been a horse. In the Middle East, even today, it would probably be a camel.