I don't always time my buys well and end up several dollars above the actual bottom. At that point I should probably take the loss and buy again on the upswing or buy another stock, but psychologically it's difficult to write it off. Holding it somehow feels like it's not lost. Sometimes it proves correct when the stock rebound a day or week later, sometimes not.
Of course, the longer I hold a loss, the greater the pressure (and stress) to write it off (opportunity cost). But every day the stock doesn't rebound is an opportunity for it to do so the next day, followed by disappointment when it doesn't. More than once I have taken the loss after weeks only to see the stock shoot up a day or two later.

the latest is BABA that went up $10 today..
I laugh at myself but I'm learning, incrementally.