I have an interesting take on this that people may find uncomfortable and totally disagree. Let me give it a shot!
Keep in mind, I am not saying this is a bad thing, but I think that sometimes sharing/giving is done for primarily selfish motives. And EVERYONE expects to receive something in return for their sharing. Whether it be as simple as feeling good about themselves, or as a passive aggressive way of exerting dominance over the receiver.
Allow me to explain, I believe that there are 2 types of sharers- the KIND Sharer and the DOMINANT Sharer. And both of these Sharers are looking for something in return for their acts of sharing.
The KIND Sharer is sharing because it makes her/him feel good. If it didn't make them feel good, they wouldn't do it.
The Dominant Sharer is sharing because it is a method to exert superiority over the receiver of the gift. It may be a very passive aggressive approach of dominance and it may not even be intentional, but this type of sharer shares because he/she wants to be noticed. Or he wants you to know that he/she has something that they receiver doesn't have, and he is so much better than you that he/she doesn't even need it.
Indeed, great points to add, thank you for the feedback.
There is usually always a reason for us to do something, so indeed if sharing wasn't to establish credibility, trust, loyalty with others, to gain credits for future help we may need in the future, or to simply be happy doing it, then we wouldn't do it like you say. The intent to appear better or get noticed for being "nice" also plays into that social reciprocity of our lives, cred for future help requested. "Look at that guy helping, he's so great, I'd help him out next time he needs help because he's helping others."
Thanks again for the good points to add.