We often feel the pressure to over-explain our boundaries.
"We can't come to dinner because the kids are tired and I have a huge project for work and the house is a mess..."
You do not need to justify protecting your family's margin. When you over-explain, you accidentally invite the other person to negotiate your boundary. They might offer solutions to your excuses, and suddenly you are trapped.
You can be warm and loving without offering a defense.
Try this instead: "Thank you so much for thinking of us, but we just aren't able to make it work this weekend."
You don't have to list your reasons to be kind. A gentle "no" is still a complete sentence. Protect your peace.