There are many reasons we need to interact with another human being.
Why introduce another person's presence? Why interact?
Here is some scenarios I tend to bring in others' presence.
Walking alone on street in NY around 2 o'clock.
When travelling, being in the cab, alone, in a new city.
Just had a nightmare and woke up.
Got a great news or ideas to share.
30 min everyday jogging in the gym.
Miss someone, wants to talk.
The reason varies from sharing ideas, passing meme, like sharing news and ideas, to trying to maximize the efficiency within the limited time, like jogging while chatting with friends; from trying to find oneself by comparing with others, interacting with others, to pursuing the sense of "real" by seeing,touching, hearing, etc; to the most basic thing: sense of safety and certainty.
I want to address the very basic reason for why interact, why need presence by focusing on safety.
When in the cab, in a strange city, for instance, the first time I went to San Jose, alone. I had no idea where the hotel was and it was dark outside, with few people on the street. When I got in the cab, I started dialing my friends' phone number, and started the conversation, and try to let the driver hear what I was talking about with my friend, such as where I was right now, in a cab, blah blah ...
I introduced my friend to be present, not only for me, to accompany myself, but also for the driver, who I was not trusting while I was struggling also in my little universe whether this man was good or bad, since I didn't have another other way if this guy was bad. Though the driver may 99% not be the bad man; and though even the driver was a bad man and was listening to my chatting with my friend in phone, he still may ignore that and be as bad as he was. even I totally understood that, I still can't help calling my friend, speaking loudly. The content is not important, the person who he/she is is also not that important. The difference between "there's someone else here", either in person or in voice , and "no one else here" matters. All is because that makes me feel safe.