Belief change has a lot to do with emotions. It's more difficult to have strong emotional impacts on other people when you aren't face to face.
It even harder when you aren't live and a person might wait between reading your posts.
Face to face to can see when a word that you say raises the level of tension in the person that you are interacting with and use that feedback to target your approach.
When I'm discussing on LessWrong I mainly focus on making arguments. When discussing in real life I take the person I'm discussing with much more into account. What are their emotional needs that I have to fulfill to get them to change their opinion?
Our instincts react to proximity / distance of other people.
Of course they are not calibrated to internet-era distances, but they probably round it to some "far enough" value. Which is probably different for text messages, for phone calls, and for video calls. (I would guess the loudness of the speakers and other technical parameters have an impact, too. Maybe even the font size.)
When I was younger, I thought that conversations in real life were much more likely to promote true beliefs and meaningful changes than conversations online, because people in real life were only willing/able to cite evidence they were actually confident in, while those online were able to easily search for arguments favoring their position.
While this is obviously wrong—the concept that people in real life only cite evidence they are justifiably confident in is comically false—I do think the dichotomy illustrated there is interesting. One thing I've noticed is that in general the "rigor" of discussions online is higher (in terms of citations, links to external content, etc.), but that conversations in real life seem still much more likely to actually change people's minds.
I have noticed this effect in both myself and others—what do you think is going on here, and how do you think we might circumvent it? If online discussions could be made more effective at causing people to actually change their minds, this could potentially prove extremely useful.