Well, I'm afraid that some adults I know haven't yet learned this particular lesson very well, actually-- and I can recall quite a number of students who didn't know it even in post-secondary...
(and to those students, I tried to gently and privately point out that such behavior in a GROUP setting was rude not only to the instructor {me} but also to one's classmates who do NOT possess that ability).
We've emphasized to DD that eye contact is an important cultural signal that one is "attentive" to the other party-- as is an interested silence while the person is speaking. DD and I both tend to avoid eye contact with others naturally if we are processing what they are SAYING to us, and I suspect that this is because their facial micro-expressions can prove quite distracting as a secondary information stream for us. This is particularly crucial when those context clues may make it more challenging to understand the SENSE of the person's intended message, or where emotional content could hinder the ability to understand.
DH doesn't have that problem, but he's not the in-person empath that she or I are, either.
Yes, this is one of those things that goes along with "this is how NT behave."
