The hardest truth - no

Explanations aren't always helpful. You think giving a reason will soften a blow, until your interlocutor pushes you more, and you find yourself blurting something out. And by this time you're angry at the other. When someone tells you no, you think that the simple refusal must have more behind it. So you ask. So you find out that you were the problem. You don't want to know that your interlocutor hates your cooking. Don't offer a kind (and probably false) explanation. Stick to your guns. When someone says no, learn to judge that the extended answer will hurt you.