Why do we share?

Maybe a better question is: why do I share? I was wondering about this while reading +Oscar Berg’s post ‘Why do people share?’.
Oscar makes several interesting statements about sharing in his post. Like this one:

The act of sharing something tells our colleagues something about us and that we think and care about what they might be interested in. If what we share is relevant and valuable to them, they will understand that we have really tried to understand what their needs and interests are. Their trust in us grows.

And, citing from an MIT Sloan article about reputation and knowledge sharing:

Reputation also plays a role where rules or systems are unable to spur sharing. Because critical information is often held privately by individuals, workers often can choose to share or withhold such information in their interactions with colleagues without fear of sanction. That leaves reputation as a key motivator in any decision to share or withhold information.

Oscar also relates to the influence of culture on sharing. Furthermore, referring to another article, the content of what you share also depends on whether you’ll share it. People share content that will bring them ‘emotional communion’ and not all content is fit for that.

And at the end of his post he points to a post by Nancy Dixon in which see distinguishes two types of knowledge sharing. One is, in my own words, work-related, the other relation-related. Examples of the first are reports. Experiences are examples of the second. More interestingly, both types of sharing have different motivations. Only the second kind of sharing was done for personal benefit.

Interesting stuff, I think. I’ve been collecting articles about knowledge sharing and blogging about his topic for some time as well. It’s not an easy topic. And the above provide interesting insights, but only scratch the surface of this topic.

At the end of Oscar’s post I was wondering what motivates Oscar to share. I can’t talk for Oscar, of course, but I will share why I share. To me there is one big reason to share information and knowledge (as far as I know them now):
Share to learn: I share what I know and see with others because I want to learn. By wording my knowledge in text or speech in itself, helps me to learn. But I also hope to learn from the response I get from the person I’m addressing or that has asked me the question. I hardly withhold information from people. I will if I think that person does not respect me or will use the information in a wrong way.

I think I can unpack this general reason and distill underlying reasons from it. These are:

1. Share to show-off: to me there is definitely a show-off element to knowledge sharing. It’s not the most important one, but I do share to show what I know, read, bump into, etc. 
2. Share to listen: an important part of learning to me is listening. So I enjoy what others are sharing, because it helps me learn. It also triggers me to share by posting things I find interesting and asking questions. 
3. Share to remember: sharing information is also a way for me to capture things I find interesting. So I bookmark a link, tweet a link or statement, etc. In this way I’ve stored it for later use. 
4. Share to be more effective: I share to learn and this helps me become more productive. Asking a question in my (digital) network, helps me find (partial) answers more quickly. Once I’ve written about something on my blog, I can refer to it later on. This makes more productive in the long run.

So, these are the reason for me to share. Do they make sense? What are your reasons to share?