Why does appreciation make us happy? Why does one crave facebook likes or a pat on the back. Our actions are always governed by this phenomenon, and I don't understand why.
From a biological viewpoint, these experiences are associated with the release of neurotransmitters like dopamine and oxytocin, which activate the "reward pathway" of the brain that is associated with feelings of happiness and mood alleviation. Since these are pleasurable experiences, we crave more and more of it, which is why a lot of our actions are governed by it. 

References:

The Science of Happiness. (2016). More Good Deeds. Retrieved 19 April 2017, from https://www.moregooddeeds.org/blog/2017/1/20/the-science-of-happiness

Fehlhaber, K. (2012). The Reward Pathway Reinforces Behavior - Knowing Neurons. Knowing Neurons. Retrieved 19 April 2017, from http://knowingneurons.com/2012/10/31/the-reward-pathway-reinforces-behavior/

Icahn School of Medicine | Neuroscience Department | Nestler Lab | Brain Reward Pathways. (2017). Neuroscience.mssm.edu. Retrieved 19 April 2017, from http://neuroscience.mssm.edu/nestler/brainRewardpathways.html

Know your brain: Reward system. (2015). Neuroscientifically Challenged. Retrieved 19 April 2017, from http://www.neuroscientificallychallenged.com/blog/know-your-brain-reward-system