For a long time I've been interested in MBTI as a teenager who was desperate to understand himself better. I even remember the moment when I first picked up the book, and looking through it to try determine what sort of career might suit my personality. That was 8 Years ago.
Over time, I eventually came to the conclusion that I was probably an ISFJ on the basis that I could identify with the basic descriptions of Si, collection and storage of internal impressions of how things around me functioned. I also identified more with the feelers than thinkers when it came to comparisons between TJs and FJs. This idea of being an ISFJ was further reinforced by searching for supporting evidence such as Si-Ti tertiary loops, underdeveloped Fe and a belief in an inferior Ne (Stress - woe is me, everything is falling apart mentality).
The main thing about the information above is that I believed I had figured it out, and had developed a fair understanding of the MBTI system. On the basis of having self-typed myself, I enjoyed the process of helping out others figure out their own type and prided myself on the ability to try and figure out people. (When I'm inaccurate, I end up wondering how I could have been wrong, if there's something faulty with my understanding of the model.)
Not knowing my own type is sort of frustrating since if I can't even accurately predict myself, how can I trust my own accuracy when it comes to typing other people. It feels like there are countless "excuses" as to why someone might be XY type (e.g. Tertiary loop, Inferior manifesting, underdeveloped function, overdeveloped function, enneagram influences, emotional stress, two functions working together to look like one, lack of awareness) that could skew the self-analysis.
I've had people tell me that I could be an ISFP, INTP, INFP, ISFJ, ESFJ, and even INFJ sometimes when I provide questionnaires and I end up being able to provide reasons "excuses" for and against why I could be that particular type.
It's come to the extent where I'm no longer even sure if my understanding of the functions, or observations of the functions are accurate. =.=