Reddit reviews The Art of SpeedReading People: How to Size People Up and Speak Their Language

The book below would certainly help clarify the difference--for those unfamiliar with it--between how extraverted feeling and introverted manifest--and hence why Trump (as an ESTP) is in the former rather than latter camp.

https://www.amazon.com/Art-SpeedReading-People-Speak-Language/dp/0316845183

At 27 I did. Wish I knew sooner because my life has been improved dramatically by acknowledging who I am rather than who I think I should be (which was largely determined by others' expectations of me).

If you want to deep dive, I'm a huge evangelist concerning the personalityhacker podcast/website -> https://personalityhacker.com/

You can find some INFP-specific podcasts on the site which can validate a lot of things in your life.

There are also some neat books that I think are great introductory/overview material to this area of study that you can probably find at your local library like the ones below. I recommend them to people that I think find MBTI-related study interesting/want another lens to look at themselves with.

(My favorite broad introduction to types. Hardly technical but accurate, I believe)
https://www.amazon.com/What-Type-Discover-Who-Really/dp/014026941X/

(Career focused one)
https://www.amazon.com/Do-What-You-Are-Personality/dp/031623673X

(One that talks about the theory in general but gives interesting suggestions on how to communicate with different types [note to self, look at what you need in conversations under your section to get your needs met conversationally])
https://www.amazon.com/Art-SpeedReading-People-Speak-Language/dp/0316845183/

(One that talks about personality types for children but can still be used to be insightful for yourself)
https://www.amazon.com/Nurture-Nature-Understand-Childs-Personality/dp/0316845132/

(Excellent book about just infps)
https://www.amazon.com/Comprehensive-INFP-Survival-Guide/dp/1945796154/

Warning: if you're an INFP and you start looking at information about other types, you will probably be constantly debating in your head as to which type you are. This is normal.

I think the best thing an INFP can do with such self knowledge is to a build a life to get their needs met without being righteously indignant (i.e. a jerk) about it when faced with resistance

The Art of Speed-Reading people suggests that it's 60% S and 40% N

You're not wrong, it can also be called Speed reading, but you need to emphasize "speed reading PEOPLE". Here's a book I found for you : http://www.amazon.com/The-Art-SpeedReading-People-Language/dp/0316845183/ref=sr_1_1?ie=UTF8&qid=1351278697&sr=8-1&keywords=the+art+of+speed+reading

EDIT : Here's another : http://www.amazon.com/What-Every-BODY-Saying-Speed-Reading/dp/0061438294/ref=pd_cp_b_0