It is all about fragility
A portrait is a window into the interior of another person. You look at the face, see the inside, and sometimes stop at the façade.
It depends on whether the person wants to reveal their plush, soft, and fragile particles to you or whether they have even sometimes forgotten to cover them up in a moment of the sheer joy of being.
I like Peter Lindbergh's statement about a portrait of a person, that it's not the physiognomy of that person, it's actually the emotions of two people who have come together to take a photograph.
