I've heard people say that "so n so will change after marriage"....OR...."so n so will change after having kids."
But I've seen people who still had the same negative habits even after marriage. I used to think that becoming a parent changes one's character completely. But, being a teacher, I've learned that this is not necessarily so. You'd be surprised at how toxic some parents can be. You wonder why a student is so troubled, and then lo and behold, you meet the parent and unlock the mystery.
Can people change? Sure. Everyone has the potential to change, but it depends on your efforts and sincerity. And you hear stories of people (substance abusers, for example) doing a complete 360 degree change.
I think that there are SOME negative qualities (being manipulative and cunning and consistently condescending) that are harder to control for some people. I've noticed that upbringing has a lot to do with how people turn out.
In my opinion, events in life such as (marriage, having children) have the potential to calm down some people and soften up their rougher edges......but if they've been consistently toxic throughout the years to others, at least some if not all of that negative essence still remains in them.