Our brains deceive us
The human brain's tendency is to constantly map its surroundings and prioritize new experiences over old ones.
According to psychologist Nick Morgan, “The brain is set up to move on, to be plastic, and to make new memories, writing them over the old...Presumably, it’s a way to stay open to new experiences, to be ready to adapt to new circumstances.”
If that person you’re talking to seems only partly present, that’s because they are!
Their brain is constantly casting about for danger and ignoring everything else.
People are only partly present during communication, with their minds distracted by safety concerns (including job safety, relationship safety, social safety, etc.).
This makes it difficult for audiences to retain information.
To effectively connect, simplify your message, be aware of safety issues, and be present yourself.