From the archive

You're not a good person. You're just afraid of conflict

You can calmly say you can't. You don't want to. You're not willing to discuss it. You're not going to lend them money. You don't have to humiliate the person asking or lecture them about your new personality. If you've already made a promise, you have to acknowledge it and deal with the consequences. If your plans have changed, let them know. Self-respect doesn't cancel out consideration for other people.