In many circumstances customs are in direct opposition to rational mindedness.
- Special event and traditional gatherings
- Belief systems about life goals, values, purpose
- Approach to a problem situation
I'm reflecting some personal biases into this thread. I've scored as an ISTJ and INTJ depending on the test. I have a curious, floaty personality and mentally ask a lot of "what if" and "what about" questions. I have a strong need for efficiency and find it painful to do tasks that intuitively feel like an inefficient use of time (it's a real chore for me to make my bed or write long articles for my website, but I can spend hours of time planning a scenario to achieve the maximum result. I have a strong dislike of (in my mind) frivolous traditions like religious functions, weddings and other celebrations. I'm the least visible person in my extended family.
But I also value facts and empirical explanations for their credibility and put a lot of study into my field. I'm loyal to a cause I believe in. I use organizational tools extensively, though my home environment is very messy.
I don't see a clear division between ISTJ and INTJ. Using myself as an example, they seem one and the same.