In debate you can’t just say “they’re wrong.” You have to say why. Same rule at the dinner table.

Asserting an error is a verdict; giving a reason is an argument, and only one of those leaves the other person anywhere to go. Without the why, all that happens is two people stating positions louder, which is how family disagreements run for years without moving an inch. Reasons also expose your own thinking to inspection, which is the uncomfortable and useful part.

At the next table disagreement, follow your objection straight away with because, and finish the sentence. If you cannot finish it, say so and ask what they are basing theirs on. That is a better conversation than the one you were about to have.