It's opportunity cost. If it goes up 10% without putting money. That's 10% you could have had if you made the right decision. The stock market going down 10%.

It's opportunity cost. If it goes up 10% without putting money. That's 10% you could have had if you made the right decision. The stock market going down 10%. That's 10% you could have had, if you made the right decision. Logically its the same. However humans loss averse, which makes one seem worse.