One would think that, when in a relationship of peers, that the unconditional support of one participant would be met with reciprocity. One would reasonably believe that if you demonstrated an unending stream of generosity and reinforcement, you could then reasonably expect the same from the recipient of it.
One would often be wrong.
Don't fool yourself, while there are Giving Trees out there willing to sacrifice and provide bedrock for Little boys, there are far more Little Boys willing to accept that support without any thought to the responsibility of returning it.
The positive spin is that people aren't often so much against you as they are for themselves. At least it isn't contempt that keeps them from upholding their end of the bargain. This is good to know when managing your expectations of them.
When my second marriage came around, someone pointed out to me that when it came to vows, my wife said a lot of lovely things but made no actual vows. No "through thick and thin, sickness and in health" sort of thing at all. It became a joke of sorts in our wedded day to day.
When I discovered that in our entire last year together she had been cheating with a friend of ours, I only had myself to blame for being surprised. She promised me nothing so I had nothing I could reasonably expect. At least not fidelity. I wasn't there for her next wedding but I hope for his sake she actually vowed something.
None of this is to say that you shouldn't be generous with those around you. It is to say that, like a Christmas present, just because you gave one doesn't mean you're getting one back. If, on the other hand, you give someone a nice Christmas present every year and never get something in return, maybe you should give a present to someone else.