Whenever you have a thought, an electrical charge is triggered, the two synapses grow together, rewiring the brain's circuitry making it easier for the thought to trigger. 

This strengthens the brain to think of that thought again. That's not great for those who have been constantly thinking negative thoughts. 

This allows one's brain to be rewired to have a more negative personality. 

Encouraging negative thoughts leads to subsequent stress, which produces a hormone called cortisol. 

Cortisol has the effect of shutting down the prefrontal cortex in our brains which is in charge of feelings such as:

• Logic
• Problem-solving 
• Empathy 
• Compassion 
• Forgiveness

The reason for this is when our brains are stressed, it redirects our resources to the Fight or Flight response.

This is great if you are in real danger but being constantly in the fight or flight responses isn't what our bodies are designed to do.

Constant triggering the fight or flight response leads to: 

• Dementia 
• Stroke 
• Heart diseases 
• Digestive issues 
• Decreases the immune system
• Lowers life expectancy.

Studies show that depression is a result of habitual negative thinking. 

This is important as people who have major depression are: 

• Twice as likely to suffer from one or more chronic diseases
• Three times as likely to suffer from pain-related disorders and injuries.
• Seven times as likely to suffer from alcohol or substance use disorders.