I first took some free online MBTI test years ago because I was into personality tests at the time, although only for fun. It said I was 50% INTJ and 50% INTP. I paid as much attention to it as I did the other personality tests (like the ones of what Disney character are you).
Then about two years ago, I randomly found another MBTI online test and took it again. I came up as INTJ. This time, I looked into it more. Since it was based off of Carl Jung, and I knew from psychology class in college that he was a well-respected psychologist, I took it more seriously, and the rest is history as far as my interest in MBTI goes.
I didn't question INTJ much for about a year since the descriptions seemed to fit me a lot (although I occasionally wondered if I was INTP). Finally, though, I started seriously wondering if I was actually an INFJ since I felt like no INTJ would be so interested in relationships and people as I am. At first, it was hard to reconcile the descriptions of INFJs with me (a lot of them are really one-sided). And also the fact that MBTI tests ask questions like "Do you value logic or emotion more?" as a determiner between F and T really threw me for a loop since I highly value logic. The clincher was when I studied the cognitive functions and realized without a doubt that Ni-Fe-Ti-Se was me. And when I realized that it wasn't unusual for INFJs to have well-developed Ti.
It's crossed my mind to test out other options, but I keep coming back to the same thing.