While the existence of the endowment effect has been comprehensively proven, no consensus has been reached so far as to what causes it. There has also been no study, as far as I can tell, that has examined whether the endowment effect is a phenomenon that is stable over time, or whether the endowment effect increases or diminishes as a function of the time someone owns an entitlement. This paper tries to answer the latter question and might provide some insight into the former (the cause of the endowment effect).