Individuals are on a daily basis in situations where they make purchasing decisions, whether they are buying high-prices products or buying low-priced products. Often decisions are taken under the influence of emotions (happiness, anger), and it can be said that the above affects the rationality of the individual when making the decision. Once the purchase decision is made, the product /service becomes the property of the customer, the user is entitled to use it. Once the product (service) is in its possession is emotionally tied to it, it is unlikely that it will be separated from it or sold. If he decides to sell it, he then becomes a seller and will appreciate the product more than the one who buys it. So, that is the subject of this graduate thesis, and this phenomenon is referred to as the endowment effect. Thus, the endowment effect leads to the fact that individuals possessing some good overestimate the value of that good because they perceive it as their property. Because of the above, there is a difference between the estimated value of the one who is willing to pay for the purchase of a particular item and who will accept to remain without the same item. This is elaborated in the theoretical part of the thesis, which includes an overview of the concepts and characteristics of behavioral economics, then psychological ownership and analysis of the endowment effect as the main part of this research. In order to prove this effect, a survey method was conducted in the empirical part of the research. Four questionnaires were created and distributed to different respondents. Each questionnaire contained a different scenario related to placing respondents in different situations related to the possession of the product /service. The endowment effect has been proven and the research hypothesis is confirmed. The thesis concludes the most important findings, the scientific and expert contribution of the work, the limitation and the proposals of future research.