Right. You first have to know the subject of the conversation and have something relevant to add to the topic.

What really aggravates me is when I'm with a group of people who are talking about something that I obviously don't know anything about, and then one of them puts me on the spot because I haven't been talking. For example, I'm with three people who all share the same job and are talking about something work related. Since I don't work with them, nor do I work in that industry, I have no idea what they're talking about and thus have nothing to add. Regardless, one of them will stop the conversation to point out that I haven't said anything, and then accuse me of being shy. And then they get all shocked and confused because they put me in a position where I have to swear at them.

On a side note, don't always assume that an extrovert is always going to be a good conversationalist. Just because someone talks a lot doesn't mean they're good at it.