Luka Doncic’s Defense

People often (justifiably) call Luka a black hole on defense. While it seems like he can play good defense at certain times like the Clipper playoff series last year, he is probably more of a negative than positive on that end of the floor.

What would he need to improve to elevate his defense to a positive or even All-NBA level? Do you think his bad defense has more to do with his limited athleticism or is it just lack of defensive instincts or effort?