It is true that there is no “unchanging self”, like a “hero” or a “coward”.
However, at a given time, a person has certain “gati” or habits/character. And one’s behavior at that time is influenced by his/her gati.
See: “The Law of Attraction, Habits, Character (Gathi), and Cravings (Asavas)” and “Habits, Goals, and Character (Gathi)“.
There are more posts on how to change one’s gati for the better. In fact, this is the key to making progress.
See, “How Habits are Formed and Broken – A Scientific View” and “Patisandhi Citta – How the Next Life is Determined According to Gathi“.
This has been discussed at various levels in many posts. You can also use the “Search” box on the top right to find more posts on gati (I have spelled it sometimes as gathi, so use both words).
Don’t hesitate to ask questions if something is not clear. It is a good question and understanding the issue can be quite helpful.