I prefer flow.

https://en.wikipedia.org/wiki/Flow_(psychology)

I don't think they're mutually exclusive.

Have you never had an interesting conversation and then looked up, realising that 4 hours had passed?

In my experience, I find it easier to focus with someone next to me than by myself. To the point that I take half as much Ritalin on pairing days than when I work alone.

Maybe you're right? It has to be the right person/people. Also, combine pairing with an open office and now you have two people with double the chances of being interrupted. So it's circumstantial.