The Grooves in Your Brain Make it hard to Change Thoughts
The older you get, the harder it is to change the thoughts in your head from negative to positive because you have created electrical pathways (or grooves) in your brain through consciously repeating thoughts over and over again. At some point, once the pathways are establishing, the thoughts go on automatic pilot outside your conscious control.
The only way to rid yourself of negative thoughts is to start as soon as you can repeating a positive thought to replace the negative thoughts in your mind. Repeating new thoughts, over and over again, will create new electrical pathways that, at some point, will become automatic habit of thoughts. Your old electrical pathways will simply dissolve because you are no longer using them.
If you are going to start changing your thoughts for the better, the time to start is now. You will notice old people become more rigid in their thinking as they get older because the electrical pathways in their brain are stronger and more resistance to change than when they were younger. - Thought Mastery