To abstract the concept people, you need the human fundamentals.
In which that everything is true in 99.99% of humans, NTs and NDs alike, past, present, and highly likely the future.
The 0.01%? That's the placeholder for the truly exceptional mysteries.
In which cannot be explained except for supernatural extremes. You may never know.
There are plenty of means to do it.
Intense study on psychology and anthropology, mystical experiences and rising consciousness, and a lot of pattern recognitions and paradoxical concepts -- the source can be a lot of social experiences, countless anecdotes and asking uncommon and exclusionary questions.
Or, do all of them.
And that's just the basics.
Then climb up and build up as you go.