It is evident that happiness is so crucial in our life. It extremely depends on people's viewpoints and individuals' ways of thinking, which make it difficult to define. On the other hand, several criteria lead people to achieve it. Happiness is one of humankind's mental states. Although people simply feel happiness, giving a comprehensive definition is complex. First, it alters from person to person. For example, for some people, going to the countryside and watching breathtaking scenery make them happy. However, for other people, playing a computer game can be happiness. Second, happiness definition changes in different places and times. In other words, an action may make a person happy in a particular place and time; however, the same action in other conditions does not bring happiness. Take watching a movie as an example; for most people, it is more enjoyable to watch in a group rather than solely. Lastly, its definition is hard to explain because it involves count...