## 2 Theoretical Background and Hypotheses
### Social-Support Activities and Subjective Well-Being  
Social support refers to the resources provided by others in a social group [15; 25]. Researchers also define social support as one's perception of being cared for, being responded to, and being helped by others in his/her social group [1; 26; 27]. By synthesizing these definitions, we recognize that social support involves resource exchange (e.g., tangible and intangible resources) between at least two persons in a social group [11; 28]. The previous literature argues that people need emotional, informational, and tangible support to help them overcome stress [1; 29]. Informational support refers to providing knowledge to solve others' problems, while emotional support refers to expressing one's concerns (e.g., caring and empathy) that could be indirectly helpful for others to solve problems [1]. On the other hand, tangible support refers to providing tangible goods or services for solving others' problems [1]. In the social media context, users usually need others' knowledge, experiences, and recommendations to help them to solve their problems [1]. They also need emotional support and encouragement to help them to deal with physical/mental problems and to cope with the stress of life changes [23]. Users may seek instrumental aid to solve their problems, as well [11]. Therefore, in this study, we considered that social support reflects the activities through which resources (e.g., information, emotional concerns, and tangible goods) will be delivered by supporters to those in need. In addition, the success of social network services (SNSs) depends largely on intensive interaction among users, including seeking support and offering support [11]. Based on the nature of social support, social support in a social unit usually involves two different types of activities: receiving support and providing support [11; 14]. In this study, we further focus on the two types of social support to reflect an individual's perception about how much help and support he/she can receive from others and the extent of an individual's involvement in providing help and support to others on social media. In this study, social-support activities were expected to positively impact subjective well-being. The previous literature suggests that one of the major motivations for people to use social media is to get help and receive emotional support [1]. Receiving helpful social support in a social unit has been considered a vital predictor of subjective well-being [7], since social support is a coping resource that helps people overcome stress and provides necessary resources for resolving a problem [16]. Moreover, [1] argue that receiving support from others brings warmth to people's hearts and helps fulfill their social needs; thus, an individual's perception of well-being can be enhanced. By synthesizing the above arguments, we propose that receiving online support from others positively impacts subjective well-being. **Hypothesis 1 (H1). **_Receiving online support is positively related to subjective well-being._  
Users of social media tend to help others or respond to other's needs, because they expect to receive important rewards [23]. For example, [30] found that users of a virtual community will help others if they feel that contributing helpful knowledge to others can enhance their professional reputations or make them feel good (i.e., enjoy helping). [31; 32] posit that self-development, altruism, and enjoyment are important factors determining users' content-contribution behavior in virtual communities. According to the uses and gratifications theory, people will seek gratification through technology use based on their needs [31]. In this sense, users who help others on social media may feel satisfied when they receive the expected rewards. The previous literature further argues that fulfilling human needs and the satisfaction of achieving goals are the basic tenets of subjective well-being [17].