In my experience, the MBTI has a good ability to single out certain personality traits and tendancies, but absolutely sucks at giving a good picture of job prospects. The simple truth is the #1 reason 95% of people find themselves in a particular job is anything but "because they had a good temperament for it." It's really only a very recent phenomenon that people have had a great deal of flexibility in what career they pursue--especially in generations past, people worked in particular jobs because their parents did, or the industry was abundant in their community, or they had kids and suddenly needed to secure income regularly, or it was a big trend in the time and place when they were going to school, etc. But how many people are there that started in law school then tried mad school, then worked as a high school teacher for a bit, and finally decided that constructionwas best for them? It doesn't happen. Nobody (at least, not a significant sample of people for developing a test like this) spends enough time trying out different career ideas, and sees each trial thorugh to a point where they can really get a good sense of what they think of the actual job environment. If you go to law school, you're probably never going to be an airline pilot, and at the time you make the decision to go to either flight school or law school, you probably lack a real thorough understanding of what the respective careers are like.
I took the Myers Briggs in a one-unit summer course called "Career Search" back in the day. They also gave a test called the STRONG indicator. The STRONG was vocation specific, and asked very specific questions about what particular interests you have. That works a bit better for vocation searching, because the people who actually do go to professional schools likely do have a very distinct and strong set of interests. So for me, with a large number of interests, I came back with my top six careers all being in the range of "very strong interest" (physician, lawyer, politician, college professor, psychologist, and engineer, not necessarily in that order). But the person next to me had their top six with three "moderate interests" and three "below average interests". People are like that--some are highly interested in many thing, and some couldn't give a rat's ass about anything.
I work in a tedious job, and when the work is tedious, I like to talk with my coworkers. This means that sometimes I find myself rambling because the other one doesn't feel like talking, so my natural inclination is to try to make them talk so that I'm not just chattering away. So I ask things like "what kind of movies do you like?" and "what kind of music do you listen to?" etc. Just today, I found myself with a complete non-talker--no answers to any questions at all. So I tried the Office Space question of "what would you do if you had a million dollars?" "Retire." "What would you do in retirement?" "I don't know, I wouldn't have to do anything." "How would you spend the time?" "I don't know, travel?" "Where would you travel?" "Gee I don't know... what's out there?"
The point is, a person like this is unlikely to find any job that they'll really love or that really gets them excited, because they clearly aren't excited by much. But they necessarily fit into one of the 16 Myers-Briggs temperaments. And people like this likely exist in every category, but if you have no passion, then no job will ever make you passionate. However, I do think that you'd find that people without strong interests are clustered in boring or menial jobs--so a test that focuses on interest can highlight the differences between people in this regard. Myers Briggs can't do it.
