When we say "Thank you", we are conveying more than the mere fact we have manners. We are conveying we appreciate what was done for us. Appreciate can come in many forms, from a simple thank you, to an outpouring of obvious gratitude.
It can mildy or greatly effect every single aspect of our lives, from our workplace to our interpersonal relationships.
Appreciation from others can directly effect how we feel about ourselves. It can make us feel loved, cared for, or even worthy when we feel appreciated. Lack of appreciation, however, can make us feel the opposite.
Not feeling appreciated can often make us question why our efforts weren't recognized which can lead to self doubt and anger towards oneself.
Our expectations of how others should respond to our efforts can be a delicate balancing act between the giver and receiver. It's probably true that for most of us, it makes us feel good to be acknowledged for the things we do.
When we feel sufficiently appreciated for those things, we are more likely to expend more of our time and energy to keep that feeling flowing. This can benefit both giver and receiver so long as no one is being taken advantage of.
There is a saying that goes "There's no such thing as altruism. No such thing as a truly selfless act. We always get paid one way or another." -- HAHA LUNG, mind control: The ancient art of psychological warfare.
I think it's safe to say the concept in that quote could apply to how far we are willing to exert ourselves to receive that appreciation for our efforts from those we most want (need) it from.
That's not to say there's anything inherently wrong about a little selfish influence when it comes to doing good things for other people, but that goes back to that delicate balancing act talked about before.
When we are successful at maintaining a healthy balance of give and take with another person, it can be a truly rewarding and pleasureable aspect of human social and interpersonal interaction.
The idea when it "works" is, the more effort you put into someone, the bigger and more satisfying the reward or payoff will be. Thus, when someone feels grateful for the efforts given to them.
However that may present itself, they will in turn somehow reciprocate that effort in a way that appeals to the other creating a stream of give and take that can bring people closer together.
Appreciation is really important in making those you love and care about feel loved and cared about. Acknowledging what has been done for us with gratitude goes a long way in creating and maintaining healthy relationships with those around us.
From strangers, to peers, to family, and perhaps most importantly, to lovers. While it may be easy for some of us to fall into a cycle of give, give, give, and no take with solid boundaries it is possible to exist in a healthy ebb and flow of appreciation with everyone in our lives.