In logic, a single negative undermines a universal affirmative.

Here's an example:

Universal affirmative:  All trees are yellow.

Single negative:  Yes, perhaps, but over there is a brown tree.

Universal affirmative:  Yeah, so what?  Who cares?

That's how marriages end.

It becomes tiresome listening to folks state universal affirmatives that easily can be undercut by a single negative.  For those who are convinced that their universal affirmative is sound, they might better argue that the greater preponderance of evidence supports their theory rather than yours.  It's Law School 101.  To win over the jury, you start with a theory and then do your best to back it up.  Science works that way, too.  One starts with an hypothesis.  The person who makes the claim must back it up with facts.  The burden is upon the claimant to provide sufficient evidence.  That's how arguments work ... or at least how they should work ... assuming the presumption of innocence ... or ignorance.  Or maybe I'm mansplaining.  I guess it depends on how you want the night to end.  A plea deal might work better.

Skepticism should be the default position in any serious disagreement.  Trust me, the best first response is to bow up, raise a wary eyebrow and say, Me?  You talking about me?  Force the person making the claim to back it up with compelling evidence.  Otherwise, it's just a bald-faced claim swinging in the wind, or, to switch metaphors, an emotional statement in search of an argument, and you defend accordingly.  Most couples work through such disagreements.  Some don't, given the evidence.  You must be the judge of that.

Anyway, I wasn't thinking about you.  My mind was on ...