let me put it this way, in a DB fashion:

+ when we react in a highly emotional way, it suggests that the accusation stings and may have some truth or validity to it

If an accusation is truly wrong and/or way off centre, then we can easily discount it as incorrect and give it no further thought.

When our spouses are highly defensive about an OP (denying there is one), we do often find that there is (at the very least) some truth and evidence.