The theory of why INFJs are theoretically supposed to be the "perfect match" for the INTP, I would appreciate input from the INFJs on the list as well, as I am focusing more on the INTP side, as I am myself an INTP and that is just plain easier.
It is my theory that within the relationship between the INTP and the INFJ, there is a grand accident that lends itself to compatibility between the two types.The INTP is most happy when allowed to rationally examine, explore, and explain his motivations and self-analysis and observation to an intimate partner. This is simply because the INTP loves self exploration, loves to gather knowledge and insight into his own actions, not for the sake of emotional discovery, simply out of a sense of curiosity and need to analyze and collect data.The INTP unemotionally and detachedly explains why he or she thinks in a certain way - that is what INTPs are best at, observation, particularly of themselves - and the INFJ then thinks that they are opening up to them, and becomes moved and emotionally attached to the INTP. The INTP sees that their observations are being received and interesting to the INFJ, so they continue. A fascinating relationship between two types. A relationship of total mutual miscommunication, the motivations are completely different, but with a reinforcing result. The INTP feels the closeness and intimacy of being able to share their scientific self-analysis, and the INFJ feels that the INTP is sharing their innermost thoughts, feelings, and emotions, and so the cycle of miscommunication keeps them locked together in a positively reenforcing relationship.