Have you ever heard of the term "neuroplasticity"? It a nutshell, it is the brain's way of creating and organizing neural pathways based on experiences throughout life. I think of neural pathways like the roads and highway system of the brain. It's not something we always have a roadmap for, so it's important to understand how the highway system works before you try to navigate blindly.
Everything that we do everyday trains our brain for a specific neural pathway. Constant stress and/or injuries create one set of neural pathways; relaxation, calm, and focus create another set. It has to do with which parts of the brain are being activated.
Rick Hanson gives an informative talk on the brain science behind neuroplasticity, but I think that he presents it in a way that we can all appreciate and understand. The video is about 7 minutes or so long, but it helps to drive home the concept that the brain can change. It can adapt and it can be shaped by the neural pathways that we train it for each day of our lives.
This is an important concept for those who have suffered from traumatic brain injuries, but it's also something equally as important for those who have had other traumatic experiences, those who suffer from post-traumatic stress, combat stress, and/or chronic daily stress. If we are having stressful experiences every single day, that's the set of neural connections that are being made most available to us. If we aren't ever activating the parts of the brain that help us to counteract stress, then when we try to access them they don't feel as available because the connection isn't as strong. This is why when someone tries meditation for the first time, they sometimes think it isn't working, when in fact it is actually working. The seeds of a new pathway are being planted. It takes time for the seeds to take root in the brain, allowing it to recognize that a new pathway is readily available to it. When you experience a positive change in the available neural pathways in the brain, you reap the rewards mentally, emotionally, and physically. It's all connected.
Watch the video below. I think you will find it interesting.