Honestly? Depends on what you mean by 'fundamentally.' Like, can someone go from being a jerk to being kind? Sure, maybe. But the underlying insecurities and wounds that made them a jerk in the first place? Those don't just vanish. You learn to manage them better, but they're still there haunting you.

I'd say it's less about whether people *can* change and more about whether they'll actually do the hard work required. The capacity is there, sure, but people are creatures of comfort and habit. My brother's been saying he'd quit drinking for five years now. Nothing's changed because he hasn't wanted it badly enough.

People absolutely can change their behaviors, beliefs, and circumstances - I've witnessed it repeatedly in my therapy practice. That said, fundamental personality traits and core temperament tend to be pretty stable across the lifespan. So you can modify your actions and perspectives, but you're probably going to be the same essential person underneath.