If you have to appeal to rare cases such as traumatic brain injury, then it is indeed 'really hard' and not of much interest theoretically or practically; the mind is what the brain does, so that massive damage can cause changes is exactly what one would have predicted already, just as one would predict that intelligence, memory, happiness, language and other cognitive traits can be changed by massive damage... (Even more massive damage can radically change one's personality through a process called 'death'.) It's not that it's an 'outlier' to be discarded, it's that it's not important if it's that rare.
I used that as an example because it's so radical as to be irrefutable, and pretty amusing. Massive personality change does not require traumatic brain injury.
Just because something is really hard does not mean it is not of much interest theoretically or practically. Everything that is meaningful in human endeavor has been "really hard."
I think that it is actually really important to study and understand personality change. Frankly, a lot of people have negative, (self)destructive personalities, and they would be much better served with positive, constructive personalities. Maybe if we understand how people change, we could come up with a consistent, efficient method to help those people, rather than shrugging and saying "haters gonna hate."
The $6m question is, is willpower itself limited by genetics? What happens then, if the ability to exert the hard effort to change the personality is itself genetically limited?
