Your brain's main job is to keep you safe and save energy. To do that, it predicts. It takes what happened before and uses it to guess what will happen next. Most of the time that's useful. It's why you can drive home without thinking about every turn.
The problem is that beliefs work the same way. If you learned early that speaking up gets you shut down, or that you have to be perfect to be accepted, your brain files that away as a rule. Years later, in a meeting or a hard conversation, it runs the rule automatically. You hold back, you over-prepare, you say yes when you mean no. You know better, and you do it anyway.
That's a limiting belief. Every time you act on it, the path gets a little deeper, like a trail worn into grass. Neuroscientists put it simply: neurons that fire together wire together.
Why insight alone doesn't fix it
Your brain has a fast alarm system, centered in a small region called the amygdala. It reacts to anything that feels like a threat in a fraction of a second, before the thinking part of your brain, the prefrontal cortex, has caught up. Under pressure, that thinking part works less well.
So in the moment that matters most, your body reacts first and your reasoning shows up late. That's why you can understand a pattern perfectly and still repeat it. The change has to reach the part of you that reacts, not only the part that reasons.