Expanding a bit on what I mean by
shared experience:
There's a huge difference between active and passive experience. Listening to a lecture is a passive experience. Asking questions is an active one. Watching TV is a passive experience. Playing a board game is an active one. The exact definitions can be a bit hazy, but the major concept should be fairly clear.
This is why in longer training courses / workshops run for a bunch of people from different communities, rather than from an already established one, there's often an 'icebreaker' game which is interactive and requires active participation, rather than just watching a funny cat video, or listening to a talk straight away. Even if the game is a little bit boring, or if you don't remember anyone's name, you have now all got at least one shared active experience, and a (slight) sense of community. If there's already a sense of community, then this is less needed, obviously. This sense of community is then useful for getting people to offer assistance to each other, be more likely to ask questions, make team discussions / activities later on much more interactive, and so on.
It's why there is a sense of community on slashdot, here, github, etc. and many many communities on reddit, youtube etc. but bbc, cnn, amazon, netflicks, etc. don't (much). Even if many many people watch BBC, or the same tv series on netflicks, and spend hours watching the same content as other people there, there's very little active participation. Often any active participation is lost amongst all the other noise, rather than becoming a shared active experience with other people. 30 people watch a glove and boots video, make their own responses, and watch each others videos, and maybe make responses to those responses. They will feel like a community. 300000 people watch it and 'like' it, and then go on to watch a video about kittens, and maybe like that too. They may enjoy their time, but won't feel like a community.