Dave: Because, maybe, it leaves us [feeling] beholden to the other.
And that can engender a sense of inferiority (e.g. why couldn't I have done it for myself?) and jealousy (why did he have so much to give when I didn't?).
No one likes to be [shown to be] inferior. No one likes to feel inferior. Therefore whoever makes one feel inferior is a target until one's self-esteem is restored: possibly by bringing down that someone who is "superior".
Sam: Why do we hate it when someone gives us far more than we can repay?
Its a power thing. I have also noted this in real life. The people who resent you most are usually the ones who also owe you the most. Generosity breeds contempt.
And it both frightens and disgusts me to need anything from anybody. I believe I should be entirely self-sufficient, at minimum. Ideally others should be able to depend on me.
So there's a lot of shame, fear, and self-contempt involved in needing assistance.
I need assistance often. This adds to the general dislike of myself.
Fran: There's an old saying that I always take to heart: Never loan a friend more money than you would be willing to simply give him, and never borrow more money from a friend than you would be comfortable accepting as a gift. This way if times get tough and the loan is not repaid, at least it will not have destroyed the friendship.
This is one of the (many) reasons why the European Christians came to hate the Jews. They had a bizarre interpretation of the Bible that seemed to say that it is a sin to loan money for interest. So when they needed to borrow money (which, oddly enough, was not a sin), the only people who would loan it to them were the Jews. They hated being in their debt, and that hatred grew into hatred for the people themselves.
My Experience: (Edward) When I resided in Winnipeg, I sponsored my wife's family in Singapore to come to Canada. Soon after almost all of her family migrated, except one, this sister did not have an education, maybe grade 3, and was not excepted, her mother begged us to do everything we could to sponsor her as a nanny for our twin boys, the night that she arrived we had a party for her. The next morning she disappeared, we discovered that she had gone to Brandon, MB with her other sister we had also sponsored. Without informing us. The family hated me to the extent that whenever they had a family together, we were never invited.
After I was Born Again at Calvary Temple Winnipeg, Junette and I would invite six people at a time for dinner, I could not understand why some of them would never even say hello to us in Church. I never did any of the above for special treatment or to be invited back for dinner, but for the love of God.
The comments from the persons above and myself may answer some of the questions you may have, after experiencing similar experiences, the bottom line is:
When you do good, give without expecting to be repaid, God sees your heart, and you will be paid back tenfold, count it all joy.