It's a cognitive bias where people feel a loss roughly 2 to 2.5 times more intensely, psychologically, than an equivalent gain. It was first proposed in Kahneman and Tversky's 1979 Prospect Theory.
Place the stop-loss order at the same moment you enter, removing the need for a real-time decision, and cap risk per trade at 1-2% so any single loss stays within an emotionally manageable size.