Bias 6: Endowment Effect
You want to go to the concert of your favorite singer. The price of the tickets is normally €30 but they are sold out. You are willing to pay up to €70 for this ticket because you really want to go to this concert. You find a ticket at this price on the Internet and buy it. The day before the concert, you discover that big fans are willing to pay up to €300 for your ticket. What do you do?
Most people prefer to keep the tickets they bought for €70 even though they could have made €300 by selling it. This is partially due to the endowment effect, the fact that we value more what we have than what we have not.
Thinking fast and slow, D.Kahneman