The decoy effect is the phenomenon where an irrelevant option is used to influence a decision between two relevant options. In the context of getting an ex back, this may manifest as trying to make yourself seem like a better option than the new person your ex is dating. However, this approach is not recommended as it can come across as manipulative and ultimately harm your efforts to win your ex back. It's important to focus solely on the connection between you and your ex and improving the quality of your interactions.