INFJ

So I just took four career/personality tests and two of them(MBTI based)said that I'm an INFJ. And the other two(not based on MBTI) indicated that I have an "enterprising personality". -Two completely paradoxical results.

I can not trust these tests (let alone the personality type theories). 8 months ago, my result of the personality test was that I was born a "dictator" ENTJ, 4 months later, an "originator" ENTP. And now they say that I'm an INFJ, the counsellor. Whilst I find quiet fitting the general description of INFJ, I shall not disregard my tendency to be susceptible towards these types of psychological categorizations.

The fact of matter is that psychology is not a well-developed science. And another fact of matter is that that very fact about psychology is bugging the holycrap out of me these days.

The question is,

Can psychology actually contribute something positive to this world, besides the personal or industrial-scale manipulators(ex. J.B Watson) and somewhat intuitive mamas who listen well?