I found that mine described me better than I could, in a few words anyway, and with some of my friends I've found ones that match perfectly, but is it meant as a general guide or is it only a few exceptions who don't fit their descriptions?
Yeah -- in most cases, the descriptions are accurate, but MBTI isn't really meant to describe personality so much as developmental patterns. After a person develops their functions past a certain point, they begin to relate with more traits of different types and may relate less to the traits of their own type.
At the base, though, you can usually expect the descriptions to be pretty darn accurate
I found that most of the INFP descriptions were about 80-85% accurate for me.
I think that apart from what gloomy-optimist said, and that everyone's an individual so no description is ever going to describe them perfectly, another thing that can contribute to it is that some of the descriptions can get confused as to what's an MBTI trait and what's an enneagram trait. There are definitely some things floating around that are described as INFP traits, but are really type 4 traits.
I think as a foundation, the INFJ description fits me extremely well. But over the past few years I have been developing massively and I have a lot of traits that INFJs are supposed lack or be weak at. In that sense, I'm definitely a "developing" INFJ. I've got to a point where I've recognised and acknowledged by weaknesses and I have come along way in strengthening them. So there are a lot of things I do that are very anti-infj but the core values and idealism is the most important aspect of our type, I reckon, and that will never go away.