Two well-studied effects explain why letting go feels like losing more than it is.
Endowment effect. Owning a thing raises its private price. People consistently demand more to give up an item than they would have paid to acquire it. The mechanism is loss aversion — the pain of losing the item is psychologically about twice as strong as the pleasure of gaining it — combined with possession becoming part of self-concept.
IKEA effect. Effort invested in a thing inflates its private value further. The bookshelf you assembled feels more valuable to you than the same bookshelf does to a buyer who did not turn the screws. Sweat equity does not transfer.
These effects are usually invisible — they feel like the item is actually worth what I think it’s worth. That confidence is exactly the failure mode. The market price, not the felt price, is what the item will recover. Almost every “I’ll sell it later” plan dies in the gap between the two.
This is also the affective barrier to the vacuum principle. Theology says release creates room for love. Psychology shows why release feels so costly: the brain is doing the math on inflated numbers it cannot see are inflated. Naming the bias is the first move; trusting an external sale price over the internal one is the second.