Before age forty the ones I've known were open minded, playful, optimistic, clever, intelligent and a bit overly eager to compromise, even where there is no disagreement. They had a subtle, but never cruel sense of humor. They were appreciative of the smallest favor or attention and just as eager to do whatever was necessary to please. Sometimes fickle, it never seemed to be a loss of affection, but rather an indecisiveness about what they needed to find happiness. Each insisted that others be honest and open in expressing feelings, but without reciprocating their own. Very secretive, they were genuinely surprised when told how little of their own thoughts and feelings they shared. Possibly a lack of self esteem(?)
After forty they seem to become anti-INFJs. I assume it's because they discover the world will not change to fit the model they've always imagined, and at first disillusioned, they become bitter, intolerant - unless challenged, inflexible - whether challenged or not, depressed and these are the things that may explain their ever increasing health problems. It's an assumption difficult to confirm, but would explain why, of all the people I've known, they suffer the greatest variety of illnesses. They also try to hide their pleasure in any misfortune suffered by those not on their approved list. As the years go by they no longer seem to believe happiness can be achieved, and will redirect any effort to offer a positive outlook. They do continue to be mysterious at times, but some effort and patience makes them reveal more about their feelings. This might be my own willingness to be direct the questions asked.
Early years they're hard to resist. Later just talking to them could probably lead to suicidal thoughts; a very slight exaggeration based on the three confirmed INFJ types I know. Considering the good, and the bad, it's been an INFJ woman that has kept me captivated for more decades than I should admit. I guess their my favorite, and least favorite, of types.