I took the test a couple of days back and was surprised it agreed with what RL folks say about me.
Personalities, however, are fluid - depending on circumstances - and dynamic as the years go on. We learn and change, sometimes for the better, sometimes for the worse, as life continually affects us. A 'personality' or social genotype can grow stronger in some areas and weaker in others.
Keep in mind, though, that age matters a lot - when younger, people tend to show vast differences in their outlook as they mature, but when much older - 40s - 60s - they tend to settle down in some persona - being either bigot or statesman, asshat or saint, and some have to carve special places on Earth to foster and keep their personalities alive. Or are run out of town or disregarded by the social groups that make up the majority of mankind.
Do some people never change?
Everyone does - they don't remain as infantile as when they were born - but some people are slow to change, maybe slow to be exposed to varied cultures, or have had less than secure childhoods, and all these can affect a person.
Should everyone be the same? Is there a personality 'better' than others?
I would disagree with that.
We need defenders, logicians, architects, soldiers, builders and destroyers, singers and storytellers - it is our diversity that is our strength and which gives power to our combined output as humanity.
Looking through the thread - it seems like we got a good team going here at GTPlanet.