Although fear can sometimes be beneficial, alerting you to real dangers, too much fear and pessimism can poison your mind with self-defeating doubt and paralyse you with indecision. You have to therefore “police” your brain, and only allow it to think thoughts which are useful, in order to keep it healthy and productive.
Consider a specific (obsessive, compulsive) fear-thought or belief that
you have been having lately. What is the benefit of allowing it to run
around in your mind?
Does it help you in any way?
Who would you be if you didn’t have it?
What would your life look like, if it did not exist?