425,744 sales of US shares were analyzed by determining which had gained value and which had lost value. Both groups were further analyzed to determine whether the shares were sold in groups or on their own.
The research found that investors were more likely to sell off losing trades in groups over those which were doing well, so as to ease the pain of loss.
Package the pain.
Releasing a whole bunch of bad news in one go is better than drip-feeding it across successive days.
Similarly, having four fillings in one go is preferable to spreading them out one a week for a month. It's less painful overall with fewer periods of worry.