"Trust" has been studied by different experts in the field of business particularly in e-business. As reasons regarding trust's importance has not been studied yet, this research concentrated on "why" trust is so important in business area. Toward this, the trust is analyzed psychologically using self-determination theory. For this purpose, deep interviews are performed which fourteen interviewees attended and responded to the questionnaires. According to the SDT, human’s needs include three different kinds psychologically; competency, relatedness, and authority. Since trust associates with the sense of cheating, resulting that sense affects the need for competency and relatedness as well. Moreover, a customer worries to be cheated by feeling a sense of incompetency where the society may have negative reactions, leading to explore the reliability by customers. Therefore, cheating has its negative influences on needs for competency and relatedness. Consequently, customer initially attempts to decrease the intermediaries before purchasing and then he/she highly will enclose his/her experience with the society.