I think feeling left out is one of the most common and powerful feelings humans face. I think fear of being left out is pretty strong too. I think it comes from being, in essence, a pack animal. In our biological roots, isolation = death, so it's something we're very sensitive to, even hints of it can provoke a lot of anxiety.

I think if you surveyed the general population, most people would report feeling left out at times. It's probably more common in people who feel depressed and anxious too, though whether that's correlation or causation is hard to say.