If you're unfamiliar with personality typing, check it out. It has its drawbacks, but it's amazingly accurate in understanding how people related to the world around them. It's based on four dichotomies and classifying people based on where they fall along them:
I'm an INTJ. We're the rarest of the types. The world tends to perceive us as strange and cold, and if you visit any forums dedicated to our type, or talk to one of us long enough, frustration with being misunderstood frequently comes up. Jiu jitsu though, has introduced me to another INTJ, BlackBeltInstructor. We tend to recognize each other quickly, and after a few conversations, I could smell the common ground. A brief summary...
To outsiders, INTJs may appear to project an aura of "definiteness", of self-confidence. This self-confidence, sometimes mistaken for simple arrogance by the less decisive, is actually of a very specific rather than a general nature; its source lies in the specialized knowledge systems that most INTJs start building at an early age. When it comes to their own areas of expertise -- and INTJs can have several -- they will be able to tell you almost immediately whether or not they can help you, and if so, how. INTJs know what they know, and perhaps still more importantly, they know what they don't know.
It's a bit strange...seeing someone who reacts to stress and boredom and attraction and uncertainty so frequently the same way that you do. It's a useful mirror though; sometimes a bit awkward, because on top of the way you learn to read each other through training together, you can also read each other's moods because they're your own.
My best friend is an INTJ, and honestly, I don't think I've struck up a friendship with another one of us in years. It was a pretty cool surprise.