Why do you post comments?

For my one hundreth post, rather than write something new about myself, I wanted to ask a question and find out: Why does anyone choose to post a comment when they read someone else's article or post?

Is the reason that you post a comment really to say that "I agree [or disagree] with what you said"? Is it to post how you have had a similar experience? Is it to encourage or discourage the person to go on a certain path? Is it to offer some advice or impart wisdom? Is it to share knowledge or how you feel? Perhaps the sentiment that "I want to be part of your life" rings true?

Maybe, the reason is less altruistic? Do you want to increase your readership? Increase the number of visits on your blog? Is the reason to badmouth someone or something? I haven't been blogging long enough to see or experience the less savory sides of this electronic medium, so it is difficult to think of other less altruistic reasons.

I like to think that I post comments because I am interested in what you have to say, as inane as it may or may not be. I want a reason to participate tangentially in the life of the person I comment to. I hope that the suggestions and advice I give are taken into consideration. I want to let you know that in some things, you are not alone.

I think that without these dreams of seeing the world, experiencing something new (and sometimes exhilarating or painful) that you've never experienced before, there wouldn't be much point in living. It's part of growing, to incorporate something new with the old.

So, do tell, why do you post comments?