@mooneevee: I have it on every site I’m on!
I think that I just get inside of my own head. So, I’ll go through phases of-
“You’re intruding on a conversation” “everyone is already friends” “no one really cares what you have to say” “the things you have to contribute are of no value”
And
“Whatever! I’ll post something and people can come talk to me if they want to!”

I feel more comfortable posting on topics with a specific conversation going on, like this one. I don’t feel comfortable hopping into a hangout.

I don’t feel like I have any way of overcoming it, I just wait until my mood swings back up into the yellow.

All of that to say, you’re not alone. 😀

Yeah, I admit that I can be a bit of a lurker at times, mostly because I have no clue what to say or how to join a conversation without feeling like I'm intruding at all.