All of us here have taken a personality type test at some point in our lives. On this particular forum, Myers-Briggs is center stage.
For some of the more elaborate systems, there can be quite a following among its practitioners. I was on forums like these for years where Myers-Briggs and the Enneagram were dissected and broken down like science experiments. In fact, there are some researchers, among them Dario Nardi and Jon Niednagel, who believe there is some neuroscientific basis for some aspects of the Myers-Briggs system (and I don't entirely disagree, but some caveats there in a little bit).
Emphasizing the Myers-Briggs since that is the system I am most familiar with, and since that is the focus of this forum, it is notable that I first took their test in 1998 or 1999 when I was a teenager. I remember coming out "INTJ," which is a common result for such a test, I've learned (even though that type is alleged to be a small part of the populace - other common test results include ISTJ, ISFJ, ESTJ, and so forth). Some of the description seemed accurate, but other parts seemed "off." Nonetheless, I thought there might be something more to the system than horoscopes, so I kept learning about it.
After awhile, I became utterly convinced I was an "INFJ" instead. I read up on all I could find, I got interested in Niednagel's "Brain Types" system that applied type to sports and linked them with motor skills (I'd heard about Brain Types before in 1997 on a sports program, but I didn't know they used the same types found in Myers-Briggs), and I was on several forums dedicated to discussion of type, including this one.
In 2011, representatives from Niednagel's Brain Types system informed me that they didn't think I was an INFJ, but that I was either INTJ, INTP, or ENTP instead, with the strongest likelihood being ENTP. That was certainly surprising to me, but when I compared my motor skills to INFJs, I could see that I fit far better the people they had in the NT categories, at any rate, whichever one I was.
To avoid bias, I then sent personality descriptions of INFJ, INTJ, INTP, and ENTP to friends who did not have any prior knowledge of Myers-Briggs or Brain Types. Again, with some surprise, every single person picked either INTP or ENTP. The consensus was that I was more of an INTP in person and more of an ENTP online.
So much for the INFJ insistence.
Still, what was the basis of all of this? How useful was such information? I could see where Niednagel's application might help in sports where motor skills are important. But could it also help me a lot in my personal life? Could it help me with jobs?
I'm afraid this is where the usefulness of the system, however much basis it may have in neuroscience in a few broad aspects, falls short. The vast majority of ENTP profiles emphasize careers where being busy, multi-tasking, and doing a ton of things at once are to my preference. Well, they are NOT to my preference - I do best at jobs where I can write a lot, be by myself, not interact with many people, and have few distractions. That would fit more of the INTP or INTJ mold. So does the insistence of several close associates that I'm tactless, unkind, and cold. However, INTP is said to have no interest or capability in multiple sports (I absolutely love sports and follow and play several) while INTJ is supposed to be very unemotional and business-oriented (bottom line type of person). Those don't apply well to me, either - I can be quite emotional and have no interest or capability in business (unlike my parents, who took naturally to it). And if we start considering INFJ again, despite the motor skill discrepancies, the sports interest and enthusiasm is again inconsistent with descriptions of the type.
And where is neuroscience in all of this? Nardi's and Niednagel's evidence is there for you to examine, but it's in its early stages at best. What's evident to me is, whatever merit there may be to some cognitive commonalities among type, it is by no means absolute. If mouth swabs or blood tests one day reveal that I fit an "ENTP" category, for instance, there will probably be more advanced testing that differentiates me from other ENTPs. We cannot assume at this juncture that all ENTPs, or any other people from a given type, all have the same talents and skills, or even weaknesses and Achilles' heels. We simply do not have that information.
It's at this point where it becomes clear that type does not necessarily determine as much in your life or your brain as its biggest adherents might like to claim. It's a tool with some uses, but don't let it run your life. We have much more to learn in the coming days.