How to stop thinking about failure

The brain is so organized that it analyses any situation from the worst possible position to prepare itself for the expected damage. 
 
This is logical because it needs to be prepared for negativity and be able to react adequately to it. 
 
Another thing is to think about the bad things all the time. Even when you start a knowingly successful event, you are already in despair and think that nothing will succeed. 
 
If you want to eliminate such thoughts, 

Write down a list of things that will be happening i.e. 
1) Valuable to you when you achieve success and 
2) Consequences of failure and 

Then Affirm every day that you will achieve the positives in the list and caution you by reading negatives in the list. 
 
📍This way you can focus on the positives of your actions, and even if everything says failure, you'll still have a chance for a good outcome.