It's just my opinion of how people should strive to live. I also would wager that the person sharing the resource will get great joy out of seeing others benefit from the sharing. A little bit of thoughtful sharing goes a long way, for both the giver and the receiver.

Why do I feel this way? That's a complicated question that I don't fully have the answer to. It probably has something to do with how humans are a social animal that has evolved to depend on each other for survival.