Been interested in MBTI for a while. There is also a lot more to it than the 4 letter code, personality description and the associated archetype. To really understand how it works you need to look at the functions the 4 letter code represents. These dictate how you absorb information, process it and make decisions. People have a preference in each of these 4 areas and of these 4 chosen preferences there are dominant, secondary, inferior and tertiary functions.

Sensing vs Intuition - Sensors are more in tune with the immediate world while intuitives look for the meaning behind events.

Feeling vs thinking - Feelers process information on a more emotional level while thinkers are more prone to rationality.

Perceiving vs judging - Perceivers are a lot happier with the free flow of things while judgers are more apt to make final decisions and conclusions on things.

Each of these preferences can be either introverted or extroverted. Extroverted is more in tune and focussed on dealing with the external world while introverted is more introspective and reserved.

For example I am an INTJ. Known as the mastermind or the sage.

The functions for an INTJ break down as follows.

Dominant - Introverted Intuition: Introverted intuition is characterized by taking small pieces of information and forming a larger picture of a system by extrapolating between these pieces. It does not focus on who, what, where and when but rather why and how.

Secondary - Extroverted thinking: Extroverted thinking is the great organizer of the outside world. It mostly focussed on how to practically do something and accomplish a goal.

Tertiary - Introverted feeling: Introverted feeling is best described as a function that tries to reconcile inner feelings with external events and actions. The best description I've heard of it in INTJ's, is a forsaken idealist stuck in the midst of a giant mechanical juggernaut.

Inferior - Extroverted sensing: Extroverted feeling is completely obsessed with external events and experiences. People with this as a dominant function are aptly described as social butterflys who thrive on sensory intake. As an inferior function it only comes out when someone is stuck in a rut, making one prone to unproductive sensory binges.

For INTJs, the combination of intuition and thinking makes for a planning juggernaught because it combines a constantly updated system roadmap with a ruthless planner and organizer. It's also a notorious shut in and doesn't have a lot of time for social customs or rituals. They're naturally confident though and the least likely type to jump on a bandwagon.