Looking at a large list of co-authors on a paper I came across, I wondered what it would look like if all of those people were ever in a room together discussing who would be first author and why. Would every author have met the others? Then I realized that I have published with a couple of people that I have never met in person for a variety of reasons. In fact, of the 12 papers I published, I counted 11 names of people that I have never met in person. I may have corresponded with them via email but I've never actually met them. That may be because I was only briefly involved to do one experiment for somebody else's paper, because there was a collaborator on my paper who figured that their department head also needed to be a co-author or because collaborators were on the other side of the world and my role in the project was never big enough to warrant going there.
What about you? How many of you co-authors have you never met in person and why?