I think expectation erodes appreciation. Even when someone is doing their job, or what may be perceived as their duty in a given relationship (i.e. the things one might typically do as a parent or partner, or friend), it is important to see someone's effort and acknowledge it. If someone feels appreciated, they are happier, and as a side benefit, more likely to do the things you like them doing.
While he was busy the other day, I did my other half's dishes and he didn't know. When he said he had to do them I said nothing, and he went out to find them done. I told him a fairy did it. 🙂 He laughed, and gave me a big hug and thanked me for doing them, even though I quite often do it and some people would come to expect it after a while. For his lack of expectation and his humble appreciation, I adore him and am more than willing to keep doing little things like that for him. Likewise I thanked him and told him how much I appreciate him for making pancakes today (he's a really good cook). He's as humble with accepting compliments as he is with accepting help, but I could see that glimmer of happiness in his eyes at knowing his effort is seen and wanted and not simply expected.
Compliments and thanks take that sense of expectation out of the things we do, and buoy us a bit, make us more willing to do them because they show it's understood we are making an effort. For my part, I always want the people in my life to know they're not looked upon as my slaves to just do their duty and that's that. The things they do for me take time or energy or money they could be spending on something they want to be doing for themselves, but they have considered me, and that means something.
