When someone gets in the way/doesn’t do what you want, the negative thoughts start to cloud your view of them, and you want to conclude that they are a bad person. You will either block out any signs of goodness and be unable to see them (from both the past and present), or you will feel conflicted when you do see goodness, because it goes against what you want to believe of them (that they are a bad person).
source: my own sinfulness.
That’s why when God calls us to love and forgive others, he is setting us free.
“Make every effort to live in peace with everyone and to be holy; without holiness no one will see the Lord. See to it that no one falls short of the grace of God and that no bitter root grows up to cause trouble and defile many.” Hebrews 12:14-15