I love the MBTI test. As someone who finds the study of personalities and psychology fascinating, I’m always interested in knowing what a person’s type is. Of the dozens of personality test I've personally tried, I prefer this one because of the variety. There are 16 distinct personality types (32 subtypes if you include the -T or -A designation), which makes it easier for everyone to find their type. I’ve also found it easier to explain to people than most other personality tests.
That said, there are definitely flaws with constantly using it to identify yourself, particularly when you box yourself in with it.
It’s not foolproof
It’s not uncommon for people to be mis-typed. Often (but not always) this is because a person doesn’t know themselves well enough to correctly answer all of the questions. For example: my ENFP sister thought she was an INFP for months because the test always gave her that result. I kept telling her she was an extrovert, but until she had heard a comprehensive explanation of the differences between extroverts and introverts, she couldn’t answer some of the questions correctly and correspondingly the test was giving her the wrong result.
Other times this is because some versions of the test have a neutral option on the questions, making it harder for the test to conclusively sort people.
Still other times it’s because an alternative testing site or book was used to type someone, instead of the ‘official’ internet/book test.
Sometimes, even when none of these apply, the online or self-administered test is still wrong. Here’s why: IT’S AN EQUATION. Every person is a unique individual, but the online test is a generalized, computer-run test. It takes your answers and computes them according to the list criteria , yes, but it’s still only an equation. Mathematics cannot accurately define a human because of the wide range of personalities and intricacies found in each person. Sometimes it takes another human that knows you well enough to help walk you through it and define you correctly.
Also, learning from just any book on the topic can be hard because many books are written by people who deal more in data than in practicality, (think of it as ‘clinical psychology’ vs ‘practical psychology’).
It can create misunderstandings
If you type an MBTI designation into Pinterest or Google, you’ll get thousands of results. But not all of them are right. (In fact, Pinterest is often the opposite of right.) What you see are usually stereotypes (often incorrect ones) or simply wrong assumptions.
For example: INFPs are often far deeper intellectually than they are portrayed. INTJs have a reputation for being hard at communication, but that’s not true either; they’re just wary of communicating with most people.
So view the results with a few grains of salt and remember that individual characteristics can’t be generalized and for each type, there is still a wide range of unique personalities.
It can lead to false representations
Leading off of the previous point, it’s easy to dislike some of the representations about your personality type and thus try to 'cross types' or represent yourself as a hybrid in an effort to escape type cliches and stereotypes.
Occasionally, there will be true MBTI hybrids, but it's pretty rare because of how specific the test is; most people usually fall into one type.
It’s better to step up and prove to people that even though you are a type typically known for flightiness (INFP for example) you are not solely defined by your type. You are more than that.
It can enable a mindset of excusing
It’s easy, especially in the American culture of today, to use your type as an excuse for your behavior. ‘well, I’m an INTJ and I’m smarter than 97% of the people I know, so it’s okay for me to be rude to them.’ No. It’s not. Hearkening back to being more than your type, no one has an excuse for being rude, inconsiderate, or downright willfully stupid.
You can utilize your personality designation without boxing yourself in. Just remember this one little fact:
It’s only one part of the puzzle
Many factors besides personality type go into determining a one’s complete personality, including but not limited to: history, background, genetic heritage, gender, family, career, and whether they are left brain or right brain.
Knowing your type can be incredibly helpful for other people to understand you or for you to understand the world around you and how you react to it. But it’s still only a part of the picture, even if it's a hugely significant part.