...is that, naturally, he's not actually a particularly angry person. His violent temper tantrums are mostly put on deliberately, as a way of inducing anger in himself through destruction similarly to his hitting his wound on Starkiller Base. Naturally, Ben Solo was quite an easy-going, optimistic sort of person, and so it's very hard for him to maintain the Dark Side - and that was why he fell in the first place, because everything he heard growing up said that evil was easy, and so if he finds the Dark Side of the Force more difficult, that must logically be the side of good according to Uncle Luke's teachings, right?
Bonus points for:
- If/when he comes back to the light, everyone's expecting...well, a lot of violent temper tantrums and easily-offended Sith. They get Ben Solo, the overgrown happy puppy.
- Finn/Kylo past relationship that ended because Finn made it harder for Kylo to stay angry.