This title is ascribed to David in 1 Sam 13.14. Yet, later in his life, he fell into serious sin. See the events recorded in 2 Sam 11. Paul is not embarrassed to refer to David (Acts 13.22). His story is in the Bible, yet he is described as a man after God’s own heart.
When David committed adultery with Bathsheba and then had her husband Uriah killed, David was acting out of character.
I think there is a contrast with Amnon and Shimeah, who appear in the narrative of David’s life. They have major and persistent character flaws.
Most people act in character most of the time; whether that is good or not so good.
An observation – I often see an item in the media where a one-off event is portrayed as a regular practice. For example, a patient dies when a nurse administers 100 times a dose. This becomes; ‘hospital staff poison patients!’ This is extremely damaging, and too common. Further it fees prejudice.
When we treat others harshly, are we considering a one-off event, an out-of-character incident, or persistent rebellion and lawless behaviour?