Regret is the emotion of counterfactuals: what you would have had if you had chosen differently. Avoiding it steers behaviour hard.
Two visible symptoms. Traders refuse to take a good setup because being wrong on a trade they chose feels worse than missing it, which is omission-bias in action. And traders hold losers rather than realise them, because closing turns an abstract loss into an event they caused.
Pre-commitment defuses it. If the rule decided the trade, the regret attaches to the rule rather than to you personally, and rules can be reviewed calmly at the weekend.
Related: omission-bias, anticipated-regret, disposition-effect