A sour or angry or cynical heart has great difficulty in seeing things properly. Their sight and conclusions about others or situations are always seen from these angles of ugliness. They find great difficulty bridling their speech when speaking to others whatever has made them with such a heart. In this ugly state of mind they take hold of any truths that support their agenda and ignores any truth that would change their heart.
When they believe they have been wronged, they cast out twenty verses that deal with "the transgression" with the intention of throwing what they have concluded as the wrong-doer down and demean them as far as they can. It doesn't seem to matter that the bulk of the texts they use aren't dealing with the situation they believe they are correct in, but they want in their heart to harm another. Forget mercy! Forget tenderness! That's what a cynical heart and bad attitude create within some.
Why does this happen? Because as long as we are angry in heart, things cannot be concluded any other way! We are unable to come to a proper perspective with a proper frame of mind because the heart is so tainted. We are unable to see anything any other way! There is something to be said that God must grant one with such a mind-set repentance (II Tim. 2:24-26). Jesus said it was God's way to send His sunshine and rain on the unjust also and His children follow His lead. It was James who penned for us that those who are unmerciful will receive no mercy.
Maybe each of us should reflect in our own hearts in light of the Lord and see, if we have a sour disposition, or angry at another or cynical in heart that we need to give that some serious thought. Wait, as long as this state of being remains within, one can't see it. They are unable until they tender themselves to the Lord and the Lord grants them to see it. Charles Dickens might have had it all right in the story he wrote called "A Christmas Carol". It wasn't Christmas that needed to be changed or the people involved. It was Scrooge!!