We all realise that our brain creates our thoughts. However in reality our thoughts create our brain too.
So how does this work? This is because every thought creates a neural connection. Therefore if you think a thought regularly enough the neural connection will grow stronger, especially if there’s an emotional attachment to it. The opposite to this is if a memory has little use, or is rarely stimulated, eventually those neural connections will largely wither away from disuse.
This is a really interesting article and discusses how stress can effect your brain and how we can get into patterns of negative thoughts called cognitive distortions.
How Your Thoughts Create Your Brain – Pick the Brain | Motivation and Self Improvement.